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The X-ray crystal structure of RadB from Thermococcus kodakaraensis KOD1, an archaeal homologue of the RecA/Rad51 family proteins, have been determined in two crystal forms. The structure represents the core ATPase domain of the RecA/ Rad51 proteins. Two independent molecules in the type 1 crystal were roughly related by 7-fold screw symmetry whereas non-crystallographic 2-fold symmetry was observed in the type 2 crystal. The dimer structure in the type 1 crystal is extended to construct a helical assembly, which resembles the filamentous structures reported for other RecA/Rad51 proteins. The molecular interface in the type 1 dimer is formed by facing a basic surface patch of one monomer to an acidic one of the other. The empty ATP binding pocket is located at the interface and barely concealed from the outside similarly to that in the active form of the RecA filament. The model assembly has a positively charged belt on one surface bordering the helical groove suitable for facile binding of DNA. Electron microscopy has revealed that, in the absence of ATP and DNA, RadB forms a filament with a similar diameter to that of the hypothetical assembly, although its helical properties were not confirmed.

The reaction center-light-harvesting 1 (RC-LH1) core complex is the photosynthetic apparatus in the membrane of the purple photosynthetic bacterium Rhodopseudomonas viridis. The RC is surrounded by an LH1 complex that is constituted of oligomers of three types of apoproteins (alpha, beta and gamma chains) with associated bacteriochlorophyll bs and carotenoid. It has been crystallized by the sitting-drop vapour-diffusion method. A promising crystal diffracted to beyond 8.0 A resolution. It belonged to space group P1, with unit-cell parameters a = 141.4, b = 136.9, c = 185.3 A, alpha = 104.6, beta = 94.0, gamma = 110.7 degrees. A Patterson function calculated using data between 15.0 and 8.0 A resolution suggested that the LH1 complex is distributed with quasi-16-fold rotational symmetry around the RC.

Maltohexaose-producing amylase, called G6-amylase (EC 3.2.1.98), from alkalophilic Bacillus sp.707 predominantly produces maltohexaose (G6) from starch and related alpha-1,4-glucans. To elucidate the reaction mechanism of G6-amylase, the enzyme activities were evaluated and crystal structures were determined for the native enzyme and its complex with pseudo-maltononaose at 2.1 and 1.9 A resolutions, respectively. The optimal condition for starch-degrading reaction activity was found at 45 degrees C and pH 8.8, and the enzyme produced G6 in a yield of more than 30% of the total products from short-chain amylose (DP = 17). The crystal structures revealed that Asp236 is a nucleophilic catalyst and Glu266 is a proton donor/acceptor. Pseudo-maltononaose occupies subsites -6 to +3 and induces the conformational change of Glu266 and Asp333 to form a salt linkage with the N-glycosidic amino group and a hydrogen bond with secondary hydroxyl groups of the cyclitol residue bound to subsite -1, respectively. The indole moiety of Trp140 is stacked on the cyclitol and 4-amino-6-deoxyglucose residues located at subsites -6 and -5 within a 4 A distance. Such a face-to-face short contact may regulate the disposition of the glucosyl residue at subsite -6 and would govern the product specificity for G6 production.

DNA primases are essential components of the DNA replication apparatus in every organism. Reported here are the biochemical characteristics of a thermostable DNA primase from the thermophilic archaeon Pyrococcus horikoshii, which formed the oligomeric unit L(1)S(1) and synthesized long DNA primers 10 times more effectively than RNA primers. The N-terminal (25KL) and C-terminal halves (20KL) of the large subunit (L) play distinct roles in regulating de novo DNA synthesis of the small catalytic subunit (S). The 25KL domain has a dual function. One function is to depress the large affinity of the intrasubunit domain 20KL for the template DNA until complex (L(1)S(1) unit) formation. The other function is to tether the L subunit tightly to the S subunit, probably to promote effective interaction between the intrasubunit domain 20KL and the active center of the S subunit. The 20KL domain is a central factor to enhance the de novo DNA synthesis activity of the catalytic S subunit since the total affinity of the L(1)S(1) unit is mainly derived from the affinity of 20KL, which is elevated more than 10 times by the heterodimer formation, presumably due to the cancellation of the inhibitory activity of 25KL through tight binding to the S subunit.

In spite of the belonging to the same c-type lysozyme family, hen egg-white lysozyme (HEWL) was much less susceptible to the dual-affinity labeling with 2′,3′-epoxypropyl β-glycoside of N-acetyllactosamine (Galβ1,4GlcNAc-Epo) than human lysozyme (HL). The three-dimensional structures of the HEWL labeled with single Galβ1,4GlcNAc-Epo and the Glu102-mutant HL labeled with double Galβ1,4GlcNAc-Epo were determined by X-ray crystallography at resolutions of 1.85 and 2.0 A, respectively. The overall conformation and the interaction mode of the carbohydrate ligand part in the singly labeled HEWL and the doubly labeled Glu102-mutant HL were basically identical to those of the correspondingly labeled wild-type HL with minor alterations in some stereochemical parameters. A detailed comparison of the structures revealed the key protein–carbohydrate and carbohydrate–carbohydrate interactions essential for the dual labeling. It was suggested that the difference in the efficiency of the dual labeling was caused by the structural difference between Gln104 in HL and Asn103 in HEWL. The relevance to our previous study and the carbohydrate–carbohydrate interaction on cell-surface membranes were discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Ultica dioica agglutinin, a plant lectin from the stinging nettle, consists of a total of seven individual isolectins. One of these structures, isolectin I, was determined at 1.9 A resolution by the X-ray method. The crystals belong to the space group P2(1) and the asymmetric unit contains two molecules related by local twofold symmetry. The molecule consists of two hevein-like chitin-binding domains lacking distinct secondary structure, but four disulfide bonds in each domain maintain the tertiary structure. The backbone structure of the two independent molecules is essentially identical and this is similarly true of the sugar-binding sites. In the crystal, the C-terminal domains bind Zn(2+) ions at the sugar-binding site. Owing to their location near a pseudo-twofold axis, the two zinc ions link the two independent molecules in a tail-to-tail arrangement: thus, His47 of molecule 1 and His67 of molecule 2 coordinate the first zinc ion, while the second zinc ion links Asp75 of molecule 1 and His47 of molecule 2.

Crystals have been grown of the V(1)-ATPase sector of the V-type ATP synthase complex (V(0)V(1)) from the thermophilic eubacterium Thermus thermophilus HB8. These crystals are grown by the vapor diffusion method in the presence of 5 mM Mg-ADP, from solutions containing 100 mM sodium acetate and 2 M sodium formate, pH 5.5. The crystals diffracted X rays beyond 3.4 A in resolution on a synchrotron radiation source. The crystals belong to the trigonal space group P3, with unit cell dimensions of a = b = 89.0 A, c = 179.2 A, and gamma = 120 degrees. The unit cell presumably contains one molecule of V(1)-ATPase and the V(m) value is calculated as 3.0 A(3)/Da.

Crystal structures of four 6-monosubstituted β-cyclodextrins, 6-deoxy-6-(1-propyl)amino-β-cyclodextrin (1), 6-deoxy-6-[(R)-1-cyclohexylethyl]amino-β-cyclodextrin (2), 6-deoxy-6-[(R)-1-phenylethyl]amino-β-cyclodextrin (3), and 6-deoxy-6-[(1R,2S)-2-hydroxyindan-1-yl]amino-β-cyclodextrin (4) were determined by X-ray analysis. In each crystal, the substituent group is inserted into the adjacent β-cyclodextrin ring from the secondary hydroxy side. This donor–acceptor type self-association through intermolecular inclusion generates a one-dimensional polymeric chain. Two types of arrangement of the β-cyclodextrin rings, a helical form and a linear form, were observed. Compounds 1 and 2 form a helically extended chain along a crystallographic twofold screw axis. In contrast the β-cyclodextrin rings are linearly stacked in the crystals of 3 and 4. The crystal packing of 3 is similar to that of a channel-type structure, while the arrangement of the β-cyclodextrin ring of 4 belongs to the cage-type. These crystal structures suggest that the self-assembly of the 6-monosubstituted β-cyclodextrins is regulated by the physical and chemical properties of the substituent group included in the adjacent β-cyclodextrin ring. A β-cyclodextrin ring with a linear and/or flexible substituent group tends to produce twofold helical packing. The inclusion of a planar and rigid group imposes restrictions on the relative orientation of the macrocycle and this causes variation in the one-dimensional arrangement depending on the shape, size, and orientation of the substituent group.

Chemically prepared hevein domains (HDs), N-terminal domain of an antifungal protein from Nicotiana tabacum (CBP20-N) and an antimicrobial peptide from Amaranthus caudatus (Ac-AMP2), were examined for their affinity for chitin, a beta-1,4-linked polymer of N-acetylglucosamine. An intact binding domain, CBP20-N, showed a higher affinity than a C-terminal truncated domain, Ac-AMP2. The formation of a pyroglutamate residue from N-terminal Gln of CBP20-N increased the affinity. The single replacement of any aromatic residue of Ac-AMP2 with Ala resulted in a significant reduction in affinity, suggesting the importance of the complete set of three aromatic residues in the ligand binding site. The mutations of Phe18 of Ac-AMP2 to the residues with larger aromatic rings, i.e. Trp, beta-(1-naphthyl)alanine or beta-(2-naphthyl)alanine, enhanced the affinity, whereas the mutation of Tyr20 to Trp reduced the affinity. The affinity of an HD for chitin might be improved by adjusting the size and substituent group of stacking aromatic rings.

Urtica dioica agglutinin is a small plant lectin that binds chitin. We purified the isolectin VI (UDA-VI) and crystal structures of the isolectin and its complex with tri-N-acetylchitotriose (NAG3) were determined by X-ray analysis. The UDA-VI consists of two domains analogous to hevein and the backbone folding of each domain is maintained by four disulfide bridges. The sequence similarity of the two domains is not high (42 %) but their backbone structures are well superimposed except some loop regions. The chitin binding sites are located on the molecular surface at both ends of the dumbbell-shape molecule. The crystal of the NAG3 complex contains two independent molecules forming a protein-sugar 2:2 complex. One NAG3 molecule is sandwiched between two independent UDA-VI molecules and the other sugar molecule is also sandwiched by one UDA-VI molecule and symmetry-related another one. The sugar binding site of N-terminal domain consists of three subsites accommodating NAG3 while two NAG residues are bound to the C-terminal domain. In each sugar-binding site, three aromatic amino acid residues and one serine residue participate to the NAG3 binding. The sugar rings bound to two subsites are stacked to the side-chain groups of tryptophan or histidine and a tyrosine residue is in face-to-face contact with an acetylamino group, to which the hydroxyl group of a serine residue is hydrogen-bonded. The third subsite of the N-terminal domain binds a NAG moiety with hydrogen bonds. The results suggest that the triad of aromatic amino acid residues is intrinsic in sugar binding of hevein-like domains.

Aromatic amino acid aminotransferase (ArATPh), which has a melting temperature of 120 degrees C, is one of the most thermostable aminotransferases yet to be discovered. The crystal structure of this aminotransferase from the hyperthermophilic archaeon Pyrococcus horikoshii was determined to a resolution of 2.1 A. ArATPh has a homodimer structure in which each subunit is composed of two domains, in a manner similar to other well characterized aminotransferases. By the least square fit after superposing on a mesophilic ArAT, the ArATPh molecule exhibits a large deviation of the main chain coordinates, three shortened alpha-helices, an elongated loop connecting two domains, and a long loop transformed from an alpha-helix, which are all factors that are likely to contribute to its hyperthermostability. The pyridine ring of the cofactor pyridoxal 5'-phosphate covalently binding to Lys(233) is stacked parallel to F121 on one side and interacts with the geminal dimethyl-CH/pi groups of Val(201) on the other side. This tight stacking against the pyridine ring probably contributes to the hyperthermostability of ArATPh. Compared with other ArATs, ArATPh has a novel substrate specificity, the order of preference being Tyr > Phe > Glu > Trp > His>> Met > Leu > Asp > Asn. Its relatively weak activity against Asp is due to lack of an arginine residue corresponding to Arg(292)* (where the asterisk indicates that this is a residues supplied by the other subunit of the dimer) in pig cytosolic aspartate aminotransferase. The enzyme recognizes the aromatic substrate by hydrophobic interaction with aromatic rings (Phe(121) and Tyr(59)*) and probably recognizes acidic substrates by a hydrophilic interaction involving a hydrogen bond network with Thr(264)*.

An Fe(III)–azido complex with the formula [Fe(cyclam)(N3)2]ClO4 (cyclam=1,4,8,11-tetraazacyclotetradecane) has been synthesized from the reaction of cis-[Fe(cyclam)Cl2]Cl with sodium azide in methanol. The X-ray structural analysis reveals that the Fe(III) atom possesses a tetragonally compressed octahedral geometry with a trans configuration of two azido ions. Variable-temperature (4.5–295 K) magnetic susceptibility measurements show that the complex is low spin over the whole temperature range. 57Fe Mossbauer spectral measurements also suggest the same spin state of the Fe(III) ion.

Crystal structures of turkey and human lysozymes were refined at atomic resolution by full-matrix least-squares method with anisotropic temperature factors. The refinement converged at the R-value of 0.104 for turkey lysozyme and 0.115 for human lysozyme at 1.12 A and 1.15 A resolution, respectively, and the estimated r.m.s. coordinate errors for respective pro-teins were 0.031 A and 0.034 A. The magnitude and the degree of anisotropy of the atomic thermal motion have strong positive correlation with the square of distance from the molecular centroid. The statistical analysis suggested that such characteristics of anisotropic thermal motion are ascribed to the rigid-body rotation and local motions rather than the breathing motion.

The turkey-egg lysozyme (TEL) complex with tri-N-acetylchitotriose [(GlcNac)3] was co-crystallized from 1.5% TEL and 2 mM (GlcNac)3 at pH 4.2. The crystal structure was determined by molecular replacement and refined to an R value of 0.182 using 10-1.77 A data. The (GlcNac)3 molecule occupies the subsites A, B and C. At the subsites B and C, the sugar residues are bound in a similar manner to that found in the hen-egg lysozyme (HEL) complex. In contrast, the GlcNac residue at the subsite A is exposed to bulk solvent and has no contact with the protein molecule because the active residue Asp101 in HEL is replaced by Gly in TEL. A sulfate ion is bound in the vicinity of subsite B and forms hydrogen bonds with the sugar residue and the guanidino group of Arg61, assisting the binding of the sugar residue to subsite B. The active-site cleft of TEL is narrower than that of native TEL, thus attaining the best fit of the (GlcNac)3 molecule. The lack of binding ability of subsite A is discussed in relation to the catalytic properties of TEL. The result suggests that the cleavage pattern of oligosaccharide substrates in the catalytic reaction is regulated by the protein-sugar interaction at subsite A.

The importance of van der Waals contact between Glu 35 and Trp 109 to the active-site structure and the catalytic properties of human lysozyme (HL) has been investigated by site-directed mutagenesis. The X-ray analysis of mutant HLs revealed that both the replacement of Glu 35 by Asp or Ala, and the replacement of Trp 109 by Phe or Ala resulted in a significant but localized change in the active-site cleft geometry. A prominent movement of the backbone structure was detected in the region of residues 110 to 120 and in the region of residues 100 to 115 for the mutations concerning Glu 35 and Trp 109, respectively. Accompanied by the displacement of the main-chain atoms with a maximal deviation of C alpha atom position ranging from 0.7 A to 1.0 A, the mutant HLs showed a remarkable change in the catalytic properties against Micrococcus luteus cell substrate as compared with native HL. Although the replacement of Glu 35 by Ala completely abolished the lytic activity, HL-Asp 35 mutant retained a weak but a certain lytic activity, showing the possible involvement of the side-chain carboxylate group of Asp 35 in the catalytic action. The kinetic consequence derived from the replacement of Trp 109 by Phe or Ala together with the result of the structural change suggested that the structural detail of the cleft lobe composed of the residues 100 to 115 centered at Ala 108 was responsible for the turnover in the reaction of HL against the bacterial cell wall substrate. The results revealed that the van der Waals contact between Glu 35 and Trp 109 was an essential determinant in the catalytic action of HL.

In order to reveal the origin of carbohydrate recognition specificity of human lysozyme by clarifying the difference in the binding mode of ligands in the active site, the inactivation of human lysozyme by 2',3'-epoxypropyl beta-glycoside derivatives of the disaccharides, N,N'-diacetylchitobiose [GlcNAc-beta-(1-->4)-GlcNAc] and N-acetyllactosamine [Gal-beta-(1-->4)-GlcNAc], was investigated and the three-dimensional structures of the affinity-labeled enzymes were determined by X-ray crystallography at 1.7 A resolution. Under the conditions comprising 2.0 x 10(-3) M labeling reagent and 1.0 x 10(-5) M human lysozyme at pH 5.4, 37 degrees C, the reaction time required to reduce the lytic activity against Micrococcus luteus cells to 50% of its initial activity was lengthened by 3.7 times through the substitution of the nonreducing end sugar residue, GlcNAc to Gal. The refined structure of human lysozyme labeled by 2',3'-epoxypropyl beta-glycoside derivatives of N,N'-diacetylchitobiose (HL/NAG-NAG-EPO complex) indicated that the interaction mode of the N,N'-diacetylchitobiose moiety in substites B and C in this study was essentially the same as in the case of the complex of human lysozyme with the free ligand. On the other hand, the hydrogen-bonding pattern and the stacking interaction at subsite B were remarkably different between the HL/NAG-NAG-EPO complex and human lysozyme labeled by the 2',3'-epoxypropyl beta-glycoside of N-acetyllactosamine (HL/GAL-NAG-EPO complex). The reduced number of possible hydrogen bonds as well as the less favorable stacking between the side chain of Tyr63 in human lysozyme and the galactose residue in the HL/GAL-NAG-EPO complex reasonably explained the less efficient ability of the 2',3'-epoxypropyl beta-glycoside of N-acetyllactosamine as compared to that of N,N'-diacetylchitobiose as an affinity labeling reagent toward human lysozyme.

Wheat germ agglutinin isolectin 3 (WGA3) was crystallized from 10 mM acetate buffer at pH 4.9 containing 6 mM CaCl(2) and 4%(v/v) ethanol. The crystal belongs to monoclinic space group P2(1) with unit-cell dimensions a = 44.86, b = 91.02, c = 44.86 A, and beta = 110.22 degrees. The asymmetric unit contains two molecules (V(m) = 2.51 A(3) Da(-1)). The crystal structure was solved by the molecular-replacement method and was refined by the simulated-annealing method. The conventional R value was 0.191 for 19713 reflections [|F(o)| > 3sigma(F)] in the resolution range 8-1.9 A. The r.m.s. deviations from the ideal bond distances and angles were 0.014 A, and 3.0 degrees, respectively, and the estimated coordinate error was 0.2-0.25 A. The two molecules in the asymmetric unit are related by the pseudo twofold symmetry and form a dimer structure. The backbone structures of the two subunits are nearly identical with the r.m.s. difference of 0.36 A for the superposition of equivalent C(alpha) atoms. The dimer structure is very similar to those of isolectins 1 and 2 with the r.m.s. difference of 0.35-0.39 A for the C(alpha) superposition. Since amino-acid residues which differ from those of isolectin 1 or 2 are not involved in the contact between the two subunits, the subunit-subunit interaction is not significantly affected by the replacement of these residues. As a result, the geometry of the sugar-binding sites which are located at the interface between the two subunit molecules is basically conserved among three isolectins.

Mono-2- O -methyl-, -2- O -ethyl-, and -2- O -allyl-cyclomaltoheptaose were prepared by alkylations of cyclomaltoheptaose in dilute aqueous alkali, and mono-2- O -propylcyclomaltoheptaose was obtained by hydrogenation of the allyl derivative. All the 2- O -alkyl derivatives were less soluble in water than was cyclomaltoheptaose. All formed inclusion complexes with toluene in aqueous solution, but only the methyl ether was less soluble in the water-toluene system than in water. The solubilities of the other ethers in water were enhanced by the addition of toluene. Partial methylation of cyclomaltoheptaose with 13 C-enriched dimethyl sulfate in dilute aqueous alkali yielded mixtures of products. The substitution patterns were analyzed by GLC-MS of the alditol acetates, prepared by hydrolysis, reduction, and acetylation, and by 13 C NMR after complete permethylation with nonenriched reagent. The results showed that methylation at O-2 is a predominant but not an exclusive reaction; as expected, the regioselectivity decreases with increasing degree of methylation.

A monoclinic crystal of hen egg lysozyme (HEL, E.C. 3.2.1.17) was obtained at 313 K from a 10%(w/v) NaCl solution at pH 7.6 containing 5%(v/v) 1-propanol. Cell dimensions were a = 27.23, b = 63.66, c = 59.12 A and beta = 92.9 degrees, and the space group was P2(1). The unit cell contains four molecules (V(m) = 1.79 A(3) Da(-1)). The structure was solved by the isomorphous replacement method with anomalous scattering followed by phase improvement by the solvent-flattening method. The refinement of the structure was carried out by the simulated-annealing method. The conventional R value was 0.187 for 18 260 reflections [|F(o)|3sigma(F)] in the resolution range 10-1.72 A. The r.m.s. deviations from the ideal bond distances and angles were 0.015 A and 3.0 degrees, respectively. The two molecules in the asymmetric unit are related by a translation of half a lattice unit along the a and c axes. The r.m.s. difference of equivalent C(alpha) atoms between the two molecules was 0.64 A and the largest difference was 3.57 A for Gly71. A significant structural change was observed in the regions of residues 45-50, 65-73 and 100-104. The residues 45-50, which connect two beta-strands, are shifted parallel to the beta-sheet plane between the two molecules. The residues 100-104 belong to the substrate-binding site (subsite A) and the high flexibility of this region may be responsible for the binding of the substrate and the release of reaction products.

A possibility of crystallography to estimate large conformational change of proteins is described. An example is the crystal structure of a mutant T4 lysozyme (Faber & Matthews, 1990), where four independent molecuels show a variety of hinge-bending angles. Another example is human α-lactalbumin (Harata & Muraki, 1992) . The amino acid residues of 104-110 assume α-helix in one crystal and a loop structure in another crystal. These observations demonstrate the large conformational flexibility of proteins and indicate that the X-ray crystallography is a powerful tool for the study of dynamic structure of proteins.

Mono-2- O -methyl-, -2- O -ethyl-, and -2- O -allyl-cyclomaltoheptaose were prepared by alkylations of cyclomaltoheptaose in dilute aqueous alkali, and mono-2- O -propylcyclomaltoheptaose was obtained by hydrogenation of the allyl derivative. All the 2- O -alkyl derivatives were less soluble in water than was cyclomaltoheptaose. All formed inclusion complexes with toluene in aqueous solution, but only the methyl ether was less soluble in the water-toluene system than in water. The solubilities of the other ethers in water were enhanced by the addition of toluene. Partial methylation of cyclomaltoheptaose with 13 C-enriched dimethyl sulfate in dilute aqueous alkali yielded mixtures of products. The substitution patterns were analyzed by GLC-MS of the alditol acetates, prepared by hydrolysis, reduction, and acetylation, and by 13 C NMR after complete permethylation with nonenriched reagent. The results showed that methylation at O-2 is a predominant but not an exclusive reaction; as expected, the regioselectivity decreases with increasing degree of methylation.

The three-dimensional structure of a modified human lysozyme (HL), Glu 53 HL, in which Asp 53 was replaced by Glu, has been determined at 1.77 A resolution by X-ray analysis. The backbone structure of Glu 53 HL is essentially the same as the structure of wild-type HL. The root mean square difference for the superposition of equivalent C alpha atoms is 0.141 A. Except for the Glu 53 residue, the structure of the active site region is largely conserved between Glu 53 HL and wild-type HL. However, the hydrogen bond network differs because of the small shift or rotation of side chain groups. The carboxyl group of Glu 53 points to the carboxyl group of Glu 35 with a distance of 4.7 A between the nearest carboxyl oxygen atoms. A water molecule links these carboxyl groups by a hydrogen bond bridge. The active site structure explains well the fact that the binding ability for substrates does not significantly differ between Glu 53 HL and wild-type HL. On the other hand, the positional and orientational change of the carboxyl group of the residue 53 caused by the mutation is considered to be responsible for the low catalytic activity (ca. 1%) of Glu 53 HL. The requirement of precise positioning for the carboxyl group suggests the possibility that the Glu 53 residue contributes more than a simple electrostatic stabilization of the intermediate in the catalysis reaction.

The functional role of tyrosine-63 in the catalytic action of human lysozyme (EC 3.2.1.17) has been probed by site-directed mutagenesis. In order to identify the role of Tyr63 in the interaction with substrate, both the three-dimensional structures and the enzymatic functions of the mutants, in which Tyr63 was converted to phenylalanine, tryptophan, leucine, or alanine, have been characterized in comparison with those of the wild-type enzyme. X-ray crystallographical analysis of the mutant enzyme at not less than 1.77-A resolution indicated no remarkable change in tertiary structure except the side chain of 63rd residue. The conversion of Tyr63 to Phe or Trp did not change the enzymatic properties against the noncharged substrate (or substrate analogs) largely, while the conversion to Leu or Ala markedly reduced the catalytic activity to a few percent of wild-type enzyme. Kinetic analysis using p-nitrophenyl penta-N-acetyl-beta-(1----4)-chitopentaoside (PNP-(GlcNAc)5) as a substrate revealed that the reduction of activity should mainly be attributed to the reduction of affinity between enzyme and substrate. The apparent contribution of the phenolic hydroxyl group and the phenol group in the side chain of Tyr63 was estimated to 0.4 +/- 0.4 and 2.5 +/- 0.8 kcal mol-1, respectively. The result suggested that the direct contact between the planar side-chain group of Tyr63 and the sugar residue at subsite B is a major determinant of binding specificity toward a electrostatically neutral substrate in the catalytic action of human lysozyme.

The direct photoisomerization of (E)-4-(1-imidazoylmethyl)-cinnamic acid (IMC), a thromboxane synthetase inhibitor, to its (Z)-isomer at pH 2.0 was decelerated by beta-cyclodextrin (beta-CyD) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD). The photostationary composition [(Z)-isomer:IMC ratio] was shifted in favor of IMC. These effects were much greater with DM-beta-CyD than with the parent beta-CyD. The quantum yield of the photoisomerization was significantly decreased by complex formation with beta-CyDs, whereas the extinction coefficient of the guest was only slightly decreased. This situation was in sharp contrast to those observed in less polar solvents and suggests that the suppressing mechanism with beta-CyD is different from that with less polar solvent systems. Spectroscopic studies (ultraviolet, circular dichroism, and nuclear magnetic resonance) indicated that IMC is tightly included in an axial mode in the cavity of DM-beta-CyD and that the rotation of the photoreactive site is sterically hindered. The results suggest that the suppressing effect of beta-CyDs on the photoisomerization of IMC results mainly from a steric origin.

Crystal structures of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CDx) complexes with m-iodophenol (MIP) and 4-biphenylacetic acid (BPA) have been determined by X-ray analysis. The macrocylic ring of TM-β-CDx is elliptically distorted in both complexes. The 2,3,6-tri-O-methylglucose residues incline against the plane through seven glycosidic oxygen atoms to relieve the steric hindrance involving methyl groups at the O(2), O(3) side. In the MIP complex, one glucose residue exhibits the skew (twist boat) conformation. The MIP molecule is fully included within the TM-β-CDx cavity, both ends of which are blocked by adjacent molecules, and the hydroxy group is hydrogen-bonded to O(2) of the host TM-β-CDx. In the BPA complex, the phenyl group is located at the centre of the cavity while half a molecule protrudes from the O(2), O(3) side. The carboxy group of BPA is located in intermolecular space to form a hydrogen bond with an adjacent TM-β-CDx molecule. The complex formation induces the chiral conformation in BPA. The biphenyl group is in the R-configuration with an angle of 42.4° between the two benzene rings.

On alkylation of cyclomaltoheptaose with oxiranes, promoted by alkali of low concentration, substitution at secondary positions, particularly at O-2, is favoured. The reaction has been used to prepare the 2-O-[(R)- and (S)-2-hydroxypropyl], 2-O-(2-hydroxy-2-methylpropyl), 2-O-[(R)- and (S)-2,3-dihydroxypropyl], and 2-O-[(R)- and (S)-2,3-dihydroxy-2-methylpropyl] derivatives. Each of these derivatives is less soluble in water than cyclomaltoheptaose, and their complexes with toluene, in contrast to that of cyclomaltoheptaose, are well soluble in water.

The role of aspartic acid 53 of human lysozyme (peptidoglycan N-acetylmuramoylhydrolase, EC 3.2.1.17) has been investigated by a site-directed mutagenesis. In order to clarify the importance of precise positioning of the negatively charged carboxylate group in the active site geometry, both the three-dimensional structure and the enzymatic function of glutamic acid 53 human lysozyme (Glu-53 human lysozyme) have been characterized in comparison with those of wild type enzyme. Glu-53 human lysozyme was crystallized and analysed by X-ray crystallography. No remarkable difference in the conformation of whole molecule except the side chain of 53rd residue was observed. In spite of full retention of the binding activities against either beta-1,4-linked trisaccharide of N-acetylglucosamine ((GlcNAc)3) or the corresponding hexasaccharide ((GlcNAc)6), the conversion of Asp-53 to Glu reduced the enzymatic activities against both bacterial cell substrate and p-nitrophenyl penta-N-acetyl-beta(1----4)-chitopentaoside (p-NO2-(GlcNAc)5) to a few percent of the activities of wild type enzyme. Calculation of electrostatic potential around the reaction center predicted that no significant change in pKa of Glu-35 was caused by the mutation. These results indicate that the precise positioning of the negatively charged carboxylate in the geometry of reaction center is essential for the rate enhancement in the catalytic action of lysozyme, and suggest that Asp-53 of human lysozyme participates in the catalytic action not simply in an electrostatical manner but partly in a nucleophilical manner.

Crystal structures of 1 : 1 inclusion complexes of hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin with (R)- and (S)-1-phenylethanol have been determined by X-ray analysis and refined to R-values of 0.077 and 0.073, respectively. In both isomorphous crystals, host molecules are arranged in a ‘head-to-tail’ mode which forms a column structure along the a-axis and guest molecules are aligned within the column. The phenyl group is inserted into the host molecule from the O(2), O(3) side and is in van der Waals contact with the inside wall of the host cavity. The hydroxyl group of the guests is hydrogen-bonded to an O(2) oxygen atom of the host. Compared with the disposition of the (S)-isomer in the host cavity, the (R)-isomer is rotated by 12° around an axis normal to the phenyl group. The geometry of the host–guest interaction indicates that the host molecule recognizes the phenyl group by the spacial fitting to the hydrophobic cavity and the hydroxy group by the hydrogen-bond formation.

Special AT-rich sequence binding protein 1 (SATB1) regulates gene expression essential in immune T-cell maturation and switching of fetal globin species, by binding to matrix attachment regions (MARs) of DNA and inducing a local chromatin remodeling. Previously we have revealed a five-helix structure of the N-terminal CUT domain, which is essentially the folded region in the MAR-binding domain, of human SATB1 by NMR. Here we determined crystal structure of the complex of the CUT domain and a MAR DNA, in which the third helix of the CUT domain deeply enters the major groove of DNA in the B-form. Bases of 5′-CTAATA-3′ sequence are contacted by this helix, through direct and water-mediated hydrogen bonds and apolar and van der Waals contacts. Mutations at conserved base-contacting residues, Gln402 and Gly403, reduced the DNA-binding activity, which confirmed the importance of the observed interactions involving these residues. A significant number of equivalent contacts are observed also for typically four-helix POU-specific domains of POU-homologous proteins, indicating that these domains share a common framework of the DNA-binding mode, recognizing partially similar DNA sequences.

An orthorhombic crystal of xylanase II from Trichoderma reesei was grown in the presence of sodium iodide. Crystal structures at atomic resolution were determined at 100 and 293 K. Protein molecules were aligned along a crystallographic twofold screw axis, forming a helically extended polymer-like chain mediated by an iodide ion. The iodide ion connected main-chain peptide groups between two adjacent molecules by an N—H\cdotsI−\cdotsH—N hydrogen-bond bridge, thus contributing to regulation of the molecular arrangement and suppression of the rigid-body motion in the crystal with high diffraction quality. The structure at 293 K showed considerable thermal motion in the loop regions connecting the β-strands that form the active-site cleft. TLS model analysis of the thermal motion and a comparison between this structure and that at 100 K suggest that the fluctuation of these loop regions is attributable to the hinge-like movement of the β-strands.

Two monoclinic crystals (space group P2(1)) of hen egg-white lysozyme, a type I crystal grown at room temperature in a D2O solution with pD 4.5 containing 2%(w/v) sodium nitrate and a type II crystal grown at 313 K in a 10%(w/v) sodium chloride solution with pH 7.6, were each transformed into another monoclinic crystal with the same space group by dehydration-induced phase transition. Changes in X-ray diffraction were recorded to monitor the progress of the crystal transformation, which started with the appearance of diffuse streaks. In both crystals, the intensity of h + l odd reflections gradually weakened and finally disappeared on completion of the transformation. X-ray diffraction in the intermediate state indicated the presence of lattices of both the native and transformed crystals. In the native type I crystal, two alternate conformations were observed in the main chain of the region Gly71-Asn74. One conformer bound a sodium ion which was replaced with a water molecule in the other conformer. In the transformed crystal, the sodium ion was removed and the main-chain conformation of this region was converted to that of the water-bound form. The transformed crystal diffracted to a higher resolution than the native crystal, while the peak width of the diffraction spots increased. Analysis of the thermal motion of protein molecules using the TLS model has shown that the enhancement of the diffraction power in the transformed crystal is mainly ascribable to the suppression of rigid-body motion owing to an increase in intermolecular contacts as a result of the loss of bulk solvent.

Caspase-activated DNase (CAD) is a key protein in the process of apoptosis that degrades DNA through the action of caspases. Its N-terminal region, the CAD domain (CAD-CD), is highly conserved among CAD family proteins and is responsible for the interaction with its inhibitor. We report here that CAD-CD spontaneously aggregates to form amyloid fibrils, without a lag time, under the conditions of low pH (below 4) and the presence of anions. Interestingly, the secondary structure of CAD-CD in the fibril state comprised not only beta-sheet but also alpha-helix, as found in CD, FTIR, and x-ray fiber diffraction experiments. Aromatic side chains have a defined orientation and are in the hydrophobic environment occurring with the CAD-CD fibrillogenesis. These findings provide new insights into the architecture of amyloid fibrils.

Bacillus thuringiensis is a valuable source of protein toxins that are specifically effective against certain insects and worms but harmless to mammals. In contrast, a protein toxin obtained from B. thuringiensis strain A1547, designated parasporin-2, is not insecticidal but has a strong cytocidal activity against human cells with markedly divergent target specificity. The 37 kDa inactive protein is proteolytically activated to a 30 kDa active form. The active form of the recombinant protein toxin was crystallized in the presence of ethylene glycol and polyethylene glycol 8000 at neutral pH. The crystals belong to the hexagonal space group P6(1) or P6(5), with unit-cell parameters a = b = 134.37, c = 121.24 A. Diffraction data from a native crystal were collected to 2.75 A resolution using a synchrotron-radiation source.

The crystal structure of the inclusion complex of cyclomaltoheptaose (beta-cyclodextrin) with hexamethylenetetramine was determined at temperatures of 123, 173, 223, and 293 K. The rigid-body motion of the host and guest molecules was evaluated by means of the TLS method that represents the molecular motion in terms of translation, libration, and screw motion. In increasing the temperature from 123 to 293 K, the amplitude of the rigid body vibration of the host molecule was increased from 1.0 to 1.3 degrees in the rotational motion and from 0.16 to 0.17 A in the translational motion. The cyclomaltoheptaose molecule has the flexibility in seven alpha-(1--4)-linkages, and each glucose unit was in the rotational vibration around an axis through two glycosidic oxygen atoms. As a result, the rigid-body parameters of cyclomaltoheptaose were considered to be overestimated because of including the contribution from the local motion of glucose units. In contrast, for the guest molecule having no structural flexibility, the TLS analysis demonstrated that the atomic thermal vibration was mostly derived from the rigid body motion. The rotational amplitude of hexamethylenetetramine was changed from 5.2 to 6.6 degrees in increasing the temperature from 123 to 293 K, while the change of the translational amplitude was from 0.20 to 0.23 A. The translational motion of the guest molecule was hindered by the inside wall of the host cavity. The molecular motion was characterized by the rotational vibration around the axis through two nitrogen atoms that were involved in the hydrogen-bond formation.

The crystal structure of the delta-cyclodextrin complex with cycloundecanone shows a channel-type structure consisting of head-to-head dimer units that include four guest molecules.

The DNA polymerase gene of the hyperthermophile Pyrococcus horikoshii was successfully overexpressed after removing an intein. The importance of an amino acid sequence around a highly conserved Asp was studied by site-directed mutagenesis. The results indicated that Lys253, Arg255, and Asp259 form a novel functional motif, K253 XRXXXD259 (outside known motifs Exo I, II, and III), that is important not only for exonuclease activity but also for polymerizing activity, confirming functional interdependence between the polymerase and exonuclease domains. The short loop region, K253G254R255, probably contributes to binding to DNA substrates. Moreover, the negative charge and the side-chain length of D259 might play a supporting role in coordinating the conserved Mg2+ to the correct position at the active center in the exonuclease domain.

Pk-REC is a protein which binds to DNA and catalyzes the central step of recombination and repair. The protein was crystallized using the hanging-drop vapour-diffusion method with PEG as a precipitant. Two orthorhombic crystal forms I and II with the same space group P2(1)2(1)2(1) were obtained at pH 8.0 using PEG 3000 and PEG 550 monomethylether, respectively. The unit-cell parameters were a = 151, b = 174, c = 241 A for form I and a = 151, b = 176, c = 300 A for form II, indicating that the asymmetric unit contains more than 20 molecules.

To get high level secretion of human lysozyme in Pichia pastoris, the following three signal sequences and one prepro sequence were evaluated: chicken lysozyme signal peptide, leucine-rich artificial signal peptide, Saccharomyces invertase signal peptide, and Saccharomyces prepro sequence of alpha factor (MF-alpha Prepro). Transformants harboring a lysozyme gene with MF-alpha Prepro secreted 20-fold more lysozyme than those harboring the lysozyme gene with any one of the other three signal sequences. Three mutant leader sequences derived from MF-alpha Prepro were constructed to discover the function of the pro region. The secretion was dramatically decreased by eliminating the pro region of MF-alpha Prepro. In contrast, MF-alpha Prepro with the EAEAEA sequence directed the secretion of an equivalent level of lysozyme having the extra amino acids (EAEAEA) in its N-terminus. For the effective secretion of native human lysozyme, MF-alpha Prepro without any spacer sequences was most suitable. The secreted protein by MF-alpha Prepro construct was identical with the authentic human lysozyme, judging from N-terminal amino acid sequencing and molecular mass spectrometric and crystallographic analysis.

The synergism between apolar and polar interactions in the carbohydrate recognition by human lysozyme (HL) was probed by site-directed mutagenesis and affinity labeling. The three-dimensional structures of the Tyr63-->Leu mutant HL labeled with 2',3'-epoxypropyl beta-glycoside of N,N'-diacetylchitobiose (L63-HL/NAG-NAG-EPO complex) and the Asp102-->Glu mutant HL labeled with the 2',3'-epoxypropyl beta-glycoside of N-acetyllactosamine were revealed by X-ray diffraction at 2.23 and 1.96 A resolution, respectively. Compared to the wild-type HL labeled with the 2', 3'-epoxypropyl beta-glycoside of N,N'-diacetylchitobiose, the N-acetylglucosamine residue at subsite B of the L63-HL/NAG-NAG-EPO complex markedly moved away from the 63rd residue, with substantial loss of hydrogen-bonding interactions. Evidently, the stacking interaction with the aromatic side chain of Tyr63 is essential in positioning the N-acetylglucosamine residue in the productive binding mode. On the other hand, the position of the galactose residue in subsite B of HL is almost unchanged by the mutation of Asp102 to Glu. Most hydrogen bonds, including the one between the carboxylate group of Glu102 and the axial 4-OH group of the galactose residue, were maintained by local movement of the backbone from residues 102-104. In both structures, the conformation of the disaccharide was conserved, reflecting an intrinsic conformational rigidity of the disaccharides. The structural analysis suggested that CH-pi interactions played an important role in the recognition of the carbohydrate residue at subsite B of HL.

Among the three kinds of the 2',3'-epoxypropyl beta-glycoside of disaccharides (GlcNAc-beta1,4-GlcNAc, Gal-beta1,4-GlcNAc, and Man-beta1,4-GlcNAc), the derivative of N-acetyllactosamine (Gal-beta1,4-GlcNAc-Epo) caused the dual labeling of human lysozyme (HL) most efficiently. The labeled HL was crystallized and analyzed by X-ray diffraction methodology. The X-ray analysis located the two Gal-beta1,4-GlcNAc-Epo moieties inside the catalytic cleft of HL. The attachment sites were the side-chain carboxylate groups of the catalytic residues Glu35 and Asp53 in HL. The first Gal-beta1, 4-GlcNAc-Epo moiety occupied virtually the same position as observed in the HL labeled with single Gal-beta1,4-GlcNAc-Epo molecule. The second Gal-beta1,4-GlcNAc-Epo moiety was recognized via the carbohydrate-carbohydrate interaction with the first Gal-beta1, 4-GlcNAc-Epo moiety in addition to the protein-carbohydrate interaction with the "right-side" catalytic cleft of HL through a number of hydrogen bonds including water-mediated ones as well as many van der Waals contacts. The two N-acetylglucosamine residues stacked with each other, while the two rings of galactose residues approximately shared the same plane. The dual labeling with two Gal-beta1,4-GlcNAc-Epo molecules was supposed to have occurred sequentially, which was accompanied with the alteration to the pKa of Glu35 derived from the esterification of Asp53 in the first labeling. Both asymmetric carbons in the connection parts between HL and N-acetyllactosamine moieties showed the same stereoconfiguration derived from the reaction with (2'R) stereoisomer concerning the epoxide group in the labeling reagent. The results demonstrated that the HL labeled with single Gal-beta1,4-GlcNAc-Epo was functional as a novel N-acetyllactosamine-binding protein, and the second labeling was performed by way of the first-ligand assisted recognition of the second ligand.

Human lysozyme (HL) labelled with the 2',3'-epoxypropyl beta-glycoside of Man-beta1,4-GlcNAc was crystallized at pH 4.5. The cell dimensions were a = 36.39, b = 116.38, c = 30.91 A and the space group was P212121. The unit cell contained four molecules (Vm = 2.18 A3 Da-1). The crystal structure was determined by molecular replacement and refined to an R value of 0.168 for 7060 reflections [|Fo| > 3sigma(F)] in the resolution range 8.0-2.1 A. A prominent shift of the Calpha-atom positions by up to 3.8 A in the region of residues 45-50 was observed compared with wild-type HL. Owing to the conformational change in this region the intermolecular contacts were altered remarkably compared to wild-type HL, explaining the difference in molecular packing. The Man-beta1,4-GlcNAc moiety occupied subsites B and C in the substrate-binding site of HL. Several differences in the hydrogen-bonded contacts between the ligand part and the protein part were observed for HL labelled with the 2',3'-epoxypropyl beta-glycoside of Man-beta1,4-GlcNAc compared with HL labelled with the corresponding derivatives of GlcNAc-beta1, 4-GlcNAc and Gal-beta1,4-GlcNAc. In contrast to the replacement of GlcNAc with Gal, the replacement of GlcNAc with Man did not sacrifice the stacking interactions with the side-chain group of Tyr63 as determined by the parallelism of the apolar face of the carbohydrate residue and the aromatic plane of the Tyr63 side chain. The 2',3'-epoxypropyl beta-glycoside of Man-beta1,4-GlcNAc exhibited almost the same affinity towards HL as Gal-beta1,4-GlcNAc, a much lower affinity than that of GlcNAc-beta1,4-GlcNAc. The difference in the protein-ligand interactions was discussed in relation to the carbo-hydrate-residue recognition specificity at subsite B of HL. The results suggested that Gln104 was a determinant for the strong recognition of GlcNAc residue at subsite B in HL.

Human lysozyme dimers were prepared by the intermolecular cross-linking of the monomer that contained the mutation of either Arg41 to Cys or Ala73 to Cys with a divalent maleimide compound. Among the three kinds of possible dimers only R41CR41C dimer, in which the two catalytic clefts can come close to each other due to the proximity of the conjugation site to the active sites, turned out to be 2.3 times more specific to a polymer substrate, ethylene glycol chitin, as compared to an oligomer substrate, PNP-(GlcNAc)5. The result indicates that it is possible to alter the substrate specificity of an enzyme by artificially controlling the orientation of the active sites.

Crystal structures of 6-O-[(R)-2-hydroxypropyl]- and 6-O-[(S)-2-hydroxypropyl]-cyclomaltoheptaose were determined by X-ray analysis. In both structures, the 2-hydroxypropyl group is inserted into the macrocyclic cavity of the next molecule related by the two-fold screw axis, and a helically extended polymeric structure is formed by repetition of the intermolecular inclusion. The hydroxyl group of the substituent group penetrates through the macrocyclic ring from the secondary hydroxyl side and is linked to an HO-6 group by a hydrogen bond. Comparison of intermolecular contacts of the substituent group indicates that the (S)-2-hydroxypropyl group is better fitted to the cavity than the (R)-2-hydroxy-propyl group.

The chiral recognition by cyclodextrins and permethylated cyclodextrins have been investigated on the basis of the X-ray data of crystalline inclusion complexes. The macrocyclic ring of α- and s-cyclo- dextrin shows a round and symmetrical structure. α-Cyclodextrin includes racemic 1-phenylethanol with the statistical disorder of the hydroxyl group. A pair of the R- and S-isomers of flurbiprofen are included within the cylindrical cavity formed by dimeric s-cyclodextrin molecules with a head-to-head arrangement. The macrocyclic ring of permethylated cyclodextrins is remarkably distorted from the regular polygonal symmetry and has more flexibility in the conformational change than cyclodextrins. Owing to the distorted conformation and steric hindrance involving methyl groups, permethylated cyclodextrins do not equally include both isomers, as demonstrated by the permethylated α-cyclodextrin complexes with mandelic acids. Permethylated α-cyclodextrin binds D-mandelic acid more tightly via a host-guest hydrogen bond and induced-fit conformational change. Permethylated s-cyclodextrin forms a hydrated crystalline complex with R-flurbiprofen, but S-flurbiprofen forms a non-hydrated crystalline complex. Significant differences between the two complexes are found in the orientation of the phenyl group and hydrogen-bond formation involving the catboxyl group.

An X-ray structure determination of heptakis(2,6-di-O-methyl)-β-cyclodextrin–2-naphthoic acid inclusion complex reveals that the naphthyl group is lengthwise inserted into the host cavity with an inclination angle of ca. 30° to the pseudosymmetry axis of the host molecule.

The crystal structure of β-cyclodextrin–hexamethylenetetramine (1:1) complex hexahydrate was determined by the X-ray diffraction method. The crystal ismonoclinic with the space group P21, Z=2, a=15.285(3), b=10.345(2), c=20.118(2) A, and β=102.14(1)°. The structure was solved by inspection of a Patterson map and the trial-and-error method combined with the rigid-body least-squares technique and refined by the block-diagonal least-squares method to the R-value of 0.056 for 4369 reflections (sinθ⁄λ

α-Cyclodextrin (α-CDx) forms a 1 : 1 complex with p-nitrophenol (p-NP) and p-hydroxybenzoic acid (p-HB). The crystal structures were determined by the X-ray method. The crystals of both complexes are orthorhombic, and the space group is P212121 with Z=4. The cell dimensions are a=13.455(1), b=15.296(1), and c=24.740(3) A for the p-NP complex, and a=13.356(1), b=15.342(1), and c=24.896(2) A for the p-HB complex. The crystal structures were determined on the basis of the isomorphous structure of the p-iodophenol complex by using 4811 reflections for the p-NP complex and 4692 reflections for the p-HB complex, and refined by the block-diagonal least-squares method to the final R-values of 0.066 and 0.067 respectively. In both complexes, the guest molecule is included in the α-CDx cavity, and the α-CDx ring is deformed from the regular hexagonal symmetry as a result of the inclusion of the planar molecule. The nitrophenyl or carboxyphenyl group is located in the cavity, while the phenolic hydroxyl group protru...

The crystal structure of the α-cyclodextrin–p-iodoaniline complex [(C6H10O5)6·C6H6NI·3H2O] has been determined by the X-ray method. The space group is P212121 with unit cell dimensions of a=13.659(2), b=15.413(3), and c=24.486(5) A. The structure was solved by the heavy-atom method and refined by least-squares techniques. The final R-value was 0.072. The p-iodoaniline molecule is included in the cavity with its axis coincident with the axis of α-cyclodextrin; the iodobenzene group is situated in the cavity, while the amino group sticks out from the cavity. The shortest contact between the α-cyclodextrin molecule and the “guest” p-iodoaniline molecule is 3.25 A, indicating that the latter is rigidly fixed in the cavity of the former. The distances between the amino group and the hydroxyl group are greater than 4.0 A; this fact well explains why the catalytic ability of α-cyclodextrin is low in the hydrolysis of para-substituted phenyl esters.

Hepatakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CDx) forms crystalline complexes with (R)-Flubiprofen (R-FP), C63H112O35C15H13O2F·H2O, and (S)-Flurbiprofen (S-FP), C63H112O35C15H13O2F. The crystal structures were determined by X-ray analysis. Crystals of both compounds are orthorhombic and the space group isP212121 with cell dimensions:a=15.092(2),b=21.714(3), andc=28.269(4) A for theR-FP complex, anda=15.271(2),b=21.451(3) andc=27.895(3) A for theS-FP complex. The macrocyclic ring of TM-β-CDx is markedly distorted because of the inability to form intramolecular hydrogen bonds and the steric hindrance involving methyl groups. In both complexes, the phenyl group is inserted into the host cavity from the O(2), O(3) side, which is wider than the O(6) side. The biphenyl moiety ofR-FP is fixed in theR-configuration within the host cavity. The phenyl group ofS-FP is disordered, andR-andS-configurations are statistically distributed with equal probability. TM-β-CDx molecules are stacked along theb axis to form a column structure. The TM-β-CDx molecule is laterally shifted with respect to the column axis, and a half of the guest molecule protrudes outside from the crevis of the column. The carboxyl group ofR-FP forms a hydrogen bond with water located outside the host cavity, while the carboxyl group ofS-FP is hydrogen-bonded to an oxygen atom of an adjacent TM-β-CDx.