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TRACKING CRYSTAL GROWTH PATTERNS ATOM BY ATOM Scientists have discovered a new mode of crystal growth at the atomic level. Researchers at the DOE's Argonne National Laboratory (ANL), Lemont, Ill., [...]

Septins constitute a group of GTP-binding proteins involved in cytokinesis and other essential cellular functions. They form heterooligomeric complexes that polymerize into nonpolar filaments and are dynamic during different stages of the cell cycle. Posttranslational modifications and interacting partners are widely accepted regulators of septin filament function, but the contribution of nucleotide is undefined due to a lack of detailed structural information. Previous low-resolution structures showed that the G domain assembles into a linear polymer with 2 different interfaces involving the N and C termini and the G binding sites. Here we report the crystal structure of SEPT2 bound to GppNHp at 2.9 A resolution. GTP binding induces conformational changes in the switch regions at the G interfaces, which are transmitted to the N-terminal helix and also affect the NC interface. Biochemical studies and sequence alignment suggest that a threonine, which is conserved in certain subgroups of septins, is responsible for GTP hydrolysis. Although this threonine is not present in yeast CDC3 and CDC11, its mutation in CDC10 and CDC12 induces temperature sensitivity. Highly conserved contact residues identified in the G interface are shown to be necessary for Cdc3-10, but not Cdc11-12, heterodimer formation and cell growth in yeast. Based on our findings, we propose that GTP binding/hydrolysis and the nature of the nucleotide influence the stability of interfaces in heterooligomeric and polymeric septins and are required for proper septin filament assembly/disassembly. These data also offer a first rationale for subdividing human septins into different functional subgroups. filament | GTP-binding protein | X-ray crystallography

The mineral eskolaite ([Cr.sub.2][O.sub.3]) has been discovered in association with natural diamond from the Udachnaya pipe in Yakutia, where it is intergrown with an octahedral diamond, mostly as an inclusion in the diamond, but also exposed at its surface. A detailed study was performed on fragments extracted from the outer surface of the diamond, using single-crystal X-ray diffraction (XRD), high-resolution electron microscopy (HRTEM), analytical electron microscopy (AEM), including line-scan and elemental-mapping, EMP, and SIMS. These applied techniques confirmed the nature of the eskolaite with 86.8 wt% [Cr.sub.2][O.sub.3] and notable impurities of Ti[O.sub.2] (3.99 wt%), [Al.sub.2][O.sub.3] (2.00 wt%), [Fe.sub.2][O.sub.3] (5.83 wt%), and MgO (1.11 wt%). Trace elements, including V (4900 ppm), Mn (129 ppm), Zr (56 ppm), and Nb (32 ppm) were also detected. The entire range of REE is just at or below the limits of detection. A small picrochromite inclusion ([X.sub.Mg] 81.2; [Y.sub.Cr] 94.7) was detected in the eskolaite; its chemistry is typical of chromite diamond inclusions. It also contains minute inclusions of perovskite, corundum, and an unidentified Ti-phase. Nano-sized cavities in picrochromite were determined to consist of carbonate and quench products, including Si, Mg, Ca, P, K, and Cl. This may represent relics of the diamond-forming metasomatic fluids. The eskolaite, containing a picrochromite inclusion, was formed at high pressure within the diamond stability field from C-O-H-bearing fluids containing Ca, K, Cl, P, and possibly even peridotitic (U-type) oxides and silicates. Keywords: Diamond association, intergrowth, eskolaite, picrochromite, Udachnaya kimberlite pipe, Yakutia, Russia

Here we report a normal-mode-based protocol for modeling anisotropic thermal motions of proteins in x-ray crystallographic refinement. The foundation for this protocol is a recently developed elastic normal mode analysis that produces much more accurate eigenvectors without the tip effect. The effectiveness of the procedure is demonstrated on the refinement of a 3.42-[Angstrom] structure of formimino-transferase cyclodeaminase, a 0.5-MDa homooctameric enzyme. Using an order of magnitude fewer adjustable thermal parameters than the conventional isotropic refinement, this protocol resulted in a decrease of the values of [R.sub.cryst] and [R.sub.free] and improvements of the density map. Several poorly resolved regions in the original isotropically refined structure became clearer so that missing side chains were fitted easily and mistraced backbone was corrected. Moreover, the distribution of anisotropic thermal ellipsoids revealed functionally important structure flexibility. This normal-mode-based refinement is an effective way of describing anisotropic thermal motions in x-ray structures and is particularly attractive for the refinement of very large and flexible supramolecular complexes at moderate resolutions. anisotropic temperature factor | conformational flexibility | elastic normal mode analysis | tip effect | x-ray crystallographic refinement

Type III secretion systems (T3SS), found in several Gram-negative pathogens, are nanomachines involved in the transport of virulence effectors directly into the cytoplasm of target cells. T3SS are essentially composed of basal membrane-embedded ring-like structures and a hollow needle formed by a single polymerized protein. Within the bacterial cytoplasm, the T3SS needle protein requires two distinct chaperones for stabilization before its secretion, without which the entire T3SS is nonfunctional. The 2.0-[Angstrom] x-ray crystal structure of the PscE-[PscF.sup.55-85]-PscG heterotrimeric complex from Pseudomonas aeruginosa reveals that the C terminus of the needle protein PscF is engulfed within the hydrophobic groove of the tetratricopeptide-like molecule PscG, indicating that the macromolecular scaffold necessary to stabilize the T3SS needle is totally distinct from chaperoned complexes between pilus- or flagellum-forming molecules. Disruption of specific PscG-PscF interactions leads to impairment of bacterial cytotoxicity toward macrophages, indicating that this essential heterotrimer, which possesses homologs in a wide variety of pathogens, is a unique attractive target for the development of novel antibacterials. bacterial pathogenicity | chaperones | x-ray crystallography

Histone demethylases, members of an emerging transcription-factor family, remove methyl groups from the lysine residues of the histone tails and thereby regulate the transcriptional activity of target genes. Structures of the catalytic-core domain of jumonji-domain-containing histone demethylase 1 (JMJD1) with and without alpha-ketoglutarate in the presence of (Fe.sup.2+) are determined by X-ray crystallography.

Hereditary coproporphyria is an autosomal dominant disorder resulting from the half-normal activity of coproporphyrinogen oxidase (CPO), a mitochondrial enzyme catalyzing the antepenultimate step in heme biosynthesis. The mechanism by which CPO catalyzes oxidative decarboxylation, in an extraordinary metal- and cofactor-independent manner, is poorly understood. Here, we report the crystal structure of human CPO at 1.58-A resolution. The structure reveals a previously uncharacterized tertiary topology comprising an unusually flat seven-stranded [beta]-sheet sandwiched by u-helices. In the biologically active dimer ([K.sub.D] = 5 x [10.sup.-7] M), one monomer rotates relative to the second by [approximately equal to] 40 [degrees] to create an intersubunit interface in close proximity to two independent enzymatic sites. The unexpected finding of citrate at the active site allows us to assign Ser-244, His-258, Asn-260, Arg-262, Asp-282, and Arg-332 as residues mediating substrate recognition and decarboxylation. We favor a mechanism in which oxygen serves as the immediate electron acceptor, and a substrate radical or a carbanion with substantial radical character participates in catalysis. Although several mutations in the CPO gene have been described, the molecular basis for how these alterations diminish enzyme activity is unknown. We show that deletion of residues (392-418) encoded by exon six disrupts dimerization. Conversely, harderoporphyria-causing K404E mutation precludes a type I [beta]-turn from retaining the substrate for the second decarboxylation cycle. Together, these findings resolve several questions regarding CPO catalysis and provide insights into hereditary coproporphyria. coproporphyrinogen oxidase | oxidative decarboxylation | mitochondria | x-ray crystallography

The iridium(perfluoropropyl)(vinyl) complex Cp(super *)Ir(PMe3)(n-C3F7)(CH=CH2) was prepared. It is characterized by X-ray crystallography, and its ground state conformation in solution was determined by (super 19)F{(super 1)H} HOESY NMR studies.

C3 exoenzymes (members of the ADP-ribosyltranferase family) are produced by Clostridium botulinum (C3bot1 and -2), Clostridium limosum (C3lim), Bacillus cereus (C3cer), and Staphylococcus aureus (C3stau1-3). These exoenzymes lack a translocation domain but are known to specifically inactivate Rho GTPases in host target cells. Here, we report the crystal structure of C3bot1 in complex with RalA (a GTPase of the Ras subfamily) and GDP at a resolution of 2.66 [Angstrom]. RalA is not ADP-ribosylated by C3 exoenzymes but inhibits ADP-ribosylation of RhoA by C3bot1, C3lim, and C3cer to different extents. The structure provides an insight into the molecular interactions between C3bot1 and RalA involving the catalytic ADP-ribosylating turn-turn (ARTT) loop from C3bot1 and helix [alpha]4 and strand [beta]6 (which are not part of the GDP-binding pocket) from RalA. The structure also suggests a molecular explanation for the different levels of C3-exoenzyme inhibition by RalA and why RhoA does not bind C3bot1 in this manner. ADP-ribosylation | protein-protein interaction | x-ray crystallography

A convenient approach to the synthesis of highly enantiomerically enriched dihydrofuran compounds via a novel retro-claisen photoarrangement is described. The scope and generality of this interesting and unusual transformation is being explored.

A unique and foremost example of a 2:1 cocrystal of mixed Cu(I)/Cu(II) complexes and a novel ferromagnetic bis(mu-hydroxo)dicopper(II) complex is presented. X-ray crystallographic techniques establish the composition of these complexes.

A total of 39 geminal dicationic ionic liquids possessing many interesting crystalline and physicochemical properties ionic liquids were synthesized. The effects of the structural variations on the physicochemical and solvation properties of the unusual class of ionic liquids are examined.

Structure of the unusual anthelmintic pyrrolobenzoxazine terpenoid natural product CJ-12662 was confirmed by X-ray crystallography and partial synthesis from 2-chloronitrobenzene. The pyrrolobenzoxazine moiety was synthesized using dye-sensitized photooxygenation of a tryptophan derivative.

2,4,6-Triphenylbenzaldehyde 1 undergoes a condensation reaction with 2-aminophenol to give N-(2',4',6'triphenylbenzylidene)-2-iminopbenol(TPIP) 2. The imine 2 can be reduced with NaB[H.sub.4] in ethanol to form N-(2',4',6'triphenylbenzyl)-2-aminophenol(TPAP) 3. Addition of trimetbylaluminum to 2 or 3 results in the formation of the complexes TPIP-Al[Me.sub.2]*AlMe.sub.3] (4) or TPAP-Al[Me.sub.2] (5). Compounds 2, 3, and 4 have been crystallographically characterized. Key words. N,O ligands, aluminum, m-terphenyl, Schiff bases, X-ray crystallography.

The thermal decarboxylation of 2-methoxycarbonyl-5-(4'-nitrophen-oxy)tetrazole (la) with the electron-rich, aromatic compounds (anisole, N,N-dimethylaniline, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene), neat or in polar solvents (DMSO, DMF, and C[H.sub.3]CN), is investigated. The solid phase thermal decomposition of a mixture of 1a, 1,3,5-trimethoxybenzene, and a Lewis acid (Alp[Cl.sub.3]) produces methyl-2,4-dimethoxysalicylate (8) in good yield, instead of the expected 2,4,6-trimethoxybenzoic acid. The X-ray structure of 8 shows intramolecular hydrogen bonds between the carbonyl oxygen and hydrogens of Me and OH groups. A measured p[K.sub.a] value of 6.8 compares well with a value of 6.4 estimated using the [C=O***H***O] hydrogen bond distances. Key words: anti-tumor, novel synthesis, X-ray structure, hydrogen bonds, computational analysis. On a etudie la decarboxylation thermique du 2-methoxycarbonyl-5-(4'-nitrophenyl)tetrazole (la) en presence de composes aromatiques riches en electrons (anisole, N,N-dimethylaniline, 1,4-dimethoxybenzene et 1,3,5-trimethoxybenzene) a l'etat pur ou dans des solvants polaires (DMSO, DMF et C[H.sub.3]CN). La decomposition thermique en phase solide d'un melange de 1a, de 1,3,5-trimethoxybenzene et d'un acide de Lewis (Al[Cl.sub.3]) conduit a la formation du 2,4-dimethoxysalicylate de methyle (8) avec un bon rendement au lieu de l'acide 2,4,6-trimethoxybenzoique attendu. La structure du compose 8 telle que determinee par diffraction des rayons X montre la presence de liaisons hydrogenes intramoleculaires entre l'oxygene du carbonyle et les atomes d'hydrogene des groupes methyle et hydroxyle. La valeur mesuree de 6,8 pour le p[K.sub.a] se compare bien avec la valeur de 6,4 evaluee sur la base des longueurs des liaisons hydrogenes [C=O***H***O]. Mots cles : antitumoral, synthese nouvelle, structure par diffraction des rayons X, liaisons hydrogenes analyse conformationnelle. [Traduit par la Redaction]

One pair of diagonal nitroxides on the calix[4]arene upper rim was found to form a strong antiferromagnetic, intramolecular dimer in solid state. Such intramolecular dimers of nitroxides could serve as a antiferromagnetic coupling unit and a building block for exchange-coupled macromolecules.

Scientists in the Crystallography Section at NIST/NBS made several outstanding contributions which greatly promoted the development and advancement of high pressure x-ray crystallography during the second-half of the 20th century. […]

Urease (urea amidohydrolase; E.C. 3.5.1.5), a nickel-dependent metalloenzyme, catalyzes the hydrolysis of urea to form ammonia and carbon dioxide (1) with a rate approximately [10.sup.14] times the rate of the [...], The crystal structure of urease from Klebsiella aerogenes has been determined at 2.2 A resolution and refined to an R factor of 18.2 percent. The enzyme contains four structural domains: three with novel folds playing structural roles, and an [(αβ).sub.8] barrel domain, which contains the bi-nickel center. The two active site nickels are 3.5 A apart. One nickel ion is coordinated by three ligands (with low occupancy of a fourth ligand) and the second is coordinated by five ligands. A carbamylated lysine provides an oxygen ligand to each nickel, explaining why carbon dioxide is required for the activation of urease apoenzyme. The structure is compatible with a catalytic mechanism whereby urea ligates Ni-1 to complete its tetrahedral coordination and a hydroxide ligand of Ni-2 attacks the carbonyl carbon. A surprisingly high structural similarity between the urease catalytic domain and that of the zinc-dependent adenosine deaminase reveals a remarkable example of active site divergence.

Calmodulin (CaM) is a 148-amino acid protein present in all eukaryotic cells that serves as the primary receptor for intracellular [Ca.sup.2t][1]. The three-dimensional structure of native CaM with four bound [...], The crystal structure of calcium-bound calmodulin (Ca sup 2+ -CaM) bound to a peptide analog of the CaM-binding region of chicken smooth muscle myosin light chain kinase has been determined and refined to a resolution of 2.4 angstroms ([Angstroms]). The structure is compact and has the shape of an ellipsoid (axial ratio 2:1). The bound CaM forms a tunnel diagonal to its long axis that engulfs the helical peptide, with the hydrophobic regions of CaM melded into a single area that closely covers the hydrophobic side of the peptide. There is a remarkably high pseudo-twofold symmetry between the closely associated domains. The central helix of the native CaM is unwound and expanded into a bend between residues 73 and 77. About 185 contacts ( 80% of this total.

Molecular recognition processes are fundamental to both humoral and cellular immunity. Despite similarities in genetics and structure[1, 2], antibodies and T cell receptors (TCR's) recognize foreign antigens differently. Antibodies bind [...], The x-ray structures of a murine MHC class I molecule ([H-2K.sup.b]) were determined in complex with two different viral peptides, derived from the vesicular stomatitis virus nucleoprotein(52-59) VSV-8, and the Sendai virus nucleoprotein(324-332), SEV-9. The [H-2K.sup.b] complexes were refined at 2.3 Å for VSV-8 and 2.5 Å for SEV-9. The structure of [H-2K.sup.b] exhibits a high degree of similarity with human HLA class I, although the individual domains can have slightly altered dispositions. Both peptides bind in extended conformations with most of their surfaces buried in the [H-2K.sup.b] binding groove. The nonamer peptide maintains the same amino- and carboxyl-terminal interactions as the octamer primarily by insertion of a bulge in the center of an otherwise β conformation. Most of the specific interactions are between side-chain atoms of [H-2K.sup.b] and main-chain atoms of peptide. This binding scheme accounts in large part for the enormous diversity of peptide sequences that bind with high affinity to class I molecules. Small but significant conformational changes in [H-2K.sub.b] are associated with peptide binding, and these synergistic movements may be an integral part of the T cell receptor recognition process.

A 3.5 angstrom resolution electron density map of the HIV-1 reverse transcriptase heterodimer complexed with nevirapine, a drug with potential for treatment of AIDS, reveals an asymmetric dimer. The polymerase [...]

Early studies on fullerene carbon clusters point to an unusual chemical reactivity of this class of molecules. Of great interest are patterns that may develop on the surfaces of these [...], [C.sub.60] and liquid bromine react to form [C.sub.60 Br.sub.24], a crystalline compound isolated as a bromine solvate, [C.sub.60 Br.24(Br.sub.2).sub.x]. The x-ray crystal structure defines of a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent [C.sub.60] framework is recognizable in [C.sub.60 Br.sub.24], but [sp.sup.3] carbons at sites of bromination distort the surface, affecting conformations of all the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 ° to 200 ° C there is effectively quantitative reversion of [C.sub.60 Br.sub.24] to [C.sub.60] and [Br.sub.2].

The x-ray structure of T4 endonuclease V, an enzyme responsible for the first step of a pyrimidine-dimer-specific excision-repair pathway, was determined at a 1.6-angstrom resolution. The enzyme consists of a [...]

Fundamental questions concerning the structural basis of antibody-antigen recognition are still largely unanswered. Although hydrogen bonding, van der Waals contacts, salt bridges, and buried surface area are of critical significance [...], The three-dimensional structure of a specific antibody (Fab 17/9) to a peptide immunogen from influenza virus hemagglutinin [HA1(75-110)] and two independent crystal complexes of this antibody with bound peptide ( [Tyr.sup.P100]-[Leu.sup.P108]) have been determined by x-ray crystallographic techniques at 2.0[angstrems], and 3.1[angstrems] resolution, respectively. The nonapeptide antigen assumes a type I β turn in the antibody combining site and interacts primarily with the Fab hypervariable loops L3, H2, and H3. Comparison of the bound and unbound Fab structures shows that a major rearrangement in the H3 loop accompanies antigen binding. This conformational change results in the creation of a binding pocket for the β turn of the peptide, allowing [Tyr.sup.P105] to be accommodated. The conformation of the peptide bound to the antibody shows similarity to its cognate sequence in the HA1, suggesting a possible mechanism for the cross-reactivity of this Fab with monomeric hemagglutinin. The structures of the free and antigen bound antibodies demonstrate the flexibility of the antibody combining site and provide an example of induced fit as a mechanism for antibody-antigen recognition.

GRAM-NEGATIVE BACTERIA PROTECT themselves from hostile environments by an outer membrane. This membrane, however, has to be permeable to polar, low molecular mass solutes including nutrients. For this purpose it [...], The integral membrane protein porin from Rhodobacter capsulatus consists of three tightly associated 16-stranded Β barrels that give rise to three distinct diffusion channels for small solutes through the outer membrane. The x-ray structure of this porin has revealed details of its shape, the residue distributions within the pore and at the membrane-facing surface, and the location of calcium sites. The electrostatic potential has been calculated and related to function. Moreover, potential calculations were found to predict the [Ca.sup.2+] sites.

MAMMALIAN MANNOSE-BINDING PROTEINS (MBP's) found in serum and liver mediate immunoglobulin-independent defensive reactions against pathogens. These proteins function by binding to specific cell-surface high-mannose oligosaccharides of various bacteria and fungi, [...], Calcium-dependent (C-type) animal lectins participate in many cell surface recognition events mediated by protein-carbohydrate interactions. The C-type lectin family includes cell adhesion molecules, endocytic receptors, and extracellular matrix proteins. Mammalian mannose-binding proteins are C-type lectins that function in antibody-independent host defense against pathogens. The crystal structure of the carbohydrate-recognition domain of a rat mannose-binding protein, determined as the holmium-substituted complex by multiwavelength anomalous dispersion (MAD) phasing, reveals an unusual fold consisting of two distinct regions, one of which contains extensive nonregular secondary structure stabilized by two holmium ions. The structure explains the conservation of 32 residues in all C-type carbohydrate-recognition domains, suggesting that the fold seen here is common to these domains. The strong anomalous scattering observed at the Ho [L.sub.III] edge demonstrates that traditional heavy atom complexes will be generally amenable to the MAD phasing method.

TRANSMEMBRANE RECEPTORS ARE THE PROTEINS THROUGH which cells and organisms commonly receive information from the outside of a cell and transmit it for processing inside the cell. One type of [...]

RECOGNITION OF COMPLEX CARBOhydrates by lectins [1] has been implicated in important biological processes such as protein targeting to cellular compartments [2], homing of leukocytes [3], and host-pathogen interactions [1]. [...]

TRANSCRIPTION FACTORS OF THE RECENTLY IDENTIFIED bZIP class, such as C/EBP, Fos, Jun, CREB, and GCN4, regulate the expression of many differnet genes in organisms as diverse as fungi, plants, [...]

ALTHOUGH THE WELL-CHARACTERized DNA binding motifs (helix-turn-helix, zinc finger, and so forth) use stably folded units of secondary structure for recognition, flexible regions can also contribute to site-specific recognition. Unfortunately, [...]

SEVERE PROTEIN-INDUCED BENDING of DUPLEX DNA HAS been demonstrated by a variety of biochemical and biophysical techniques [1-10], including a low-resolution crystal structure of the nucleosome core particle [10]. Current [...]

THE PRINCIPAL BIOLOGICAL ROLE OF ACETYLCHOLINE-sterase (AChE, acetylcholine hydrolase, E.C. 3.1.1.7) is termination of impulse transmission at cholinergic synapses by rapid hydrolysis of the neurotransmitter acetylcholine (ACh) (1). [CH.SUB.3.COOCH.SUB.2.CH.SUB.2.N.SUP.+.(CH.SUB.3.).SUB.3] + [...]

OLIGOSACCHARIDE EPITOPES OF bacterial and tumor cell-surface carbohydrates are important disease markers [1] and targets for therapeutic antibodies [2], but to date a crystal structure for an antibody-carbohydrate complex has [...]

NITRITE REDUCTASES (NIRs) ARE part of a denitrification pathway in which nitrate is sequentially reduced to nitrite, nitric oxide, nitrous oxide, and dinitrogen ([NO.sub.2.sup.-] → NO → [N.sub.2.O] → [N.sub.2]) [...]

THE PROBLEM OF HOW, DURING PROTEIN PHOSPHORYLATION, a targeted protein substrate is recognized by a specific protein kinase has been particularly elusive because the determinants for peptide recognition are widely [...]

PROTEIN PHOSPHORYLATION AS A MECHANISM FOR REGULATING protein activity was first recognized with glycogen phosphorylase [1,2]. Now after over three decades, it is clear that this mechanism for the reversible [...]

IN AN ACCOMPANYING REPORT [1], THE function of FKBP [2, 3] was discussed, and its structure, determined by nuclear Overhauser effect (NOE)-restrained molecular dynamics, was described. After this structure had [...]

The x-ray crystal structure of recombinant human interferon- [Gamma] has been determined with the use of multiple-isomorphous-replacement techniques. Interferon- [Gamma], which is dimeric in solution, crystallizes with two dinners related [...]

An ab initio approach to the phase problem in macromolecular x-ray crystallography is described. A random gas of hard-sphere point scatterers is allowed to condense under the constraint of the [...]

FIBROBLAST GROWTH FACTORS (FGFs) are members of a protein family that induce mitogenic, chemotactic, and angiogenic activity in a variety of cells of epithelial, mesenchymal, and neural origins (1). As [...]

The crystal structure of a complex between a phosphonate transition-state analogue and the phospholipase [A.sub.2] ([PLA.sub.2]) from Naja naja atra venom has been solved and refined to a resolution of [...]

The reaction of Cr[Cl.sub.3] with three equivalents of the lithium salt of [R-(R *,R *)]-(+)-bis([alpha]-methylbenzyl)amine produces the trigonal planar Cr(III) tris(amido) complex. The X-ray structure of Cr[[N[{CH(Me)Ph}.sub.2]].sub.3] is reported. Key words: chromium, X-ray crystal structure, amido ligands, chiral ligands.

To Eva Pebay-Peyroula and other x-ray crystallographers, bacteriorhodopsin has brought 20 years of frustration. Beginning in the mid-1970s, researchers managed to coax this large protein (which helps convert sunlight to [...]

Cyclosporin A (CsA), an immunosuppressive drug that acts as inhibitor of T cell activation[1], forms a complex in vivo with cyclophilin (CYP)[2], a cis-trans isomerase, and can inhibit its activity [...], The conformation of the immunosuprressive drug cyclosporin A (CsA) in a complex with a Fab molecule has been established by crystallographic analysis to 2.65 angstrom resolution. This conformation of CsA is similar to that recently observed in the complex with the rotamase cyclophilin, its binding protein in vivo, and totally different from it conformation in an isolated form as determined from x-ray and nuclear magnetic resonance analysis. Because the surfaces of CsA interacting with cyclophilin or with the Fab are not identical, these results suggest that the conformation of CsA observed in the bound form preexists in aqueous solution and is not produced by interaction with the proteins.

THE RECENTLY DEVELOPED LARGE-scale production [1, 2] and separation [3] methods for the all-carbon molecules [C.sub.60], [C.sub.70], [C.sub.76/78], [C.sub.84], and [C.sub.94] (fullerenes) have opened up new vistas in organic and [...]

A MATERIALS FABRICATION TECHnique has been developed that provides the ability to draw ultrafine metallic filaments. Previously, very fine wires of metals could be drawn at a temperature at which [...]

The dinuclear gold complexes are prepared and characterized by using X-ray crystallography. The photophysical studies have shown that the participation of intra- and intermolecular Au...Au interactions are relevant to the luminescent properties and the emission spectra are strongly temperature dependent.