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Bei Tauben erzeugt intravenos gegebenes Alloxan bekanntlich Lasionen, die denen der Eingeweidegicht ahneln. Chemische und mikroskopische Untersuchungen zeigten eine grose Menge von Uraten auf Perikardium, Peritoneum und Pleura. Die grose Zunahme der Harnsaure im Blute, die von anderen Autoren kolorimetrisch festgestellt wurde, wird durch die Urikasemethode bestatigt. In der vorliegenden Mitteilung wird weiterhin uber ein der Gelenkgicht ahnliches Bild bei alloxanbehandelten Tauben berichtet. Verschiedene Tierarten mit einem «ureotelic-proteic metabolism» zeigen nach Alloxan weder eine nennenswerte Harnsaurezunahme im Blut noch eine Gicht der Eingeweide oder der Gelenke.

We report here the synthesis and the conformation analysis by (1)H NMR spectroscopy and computer simulations of six potent sweet molecules, N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-S-tert-butyl-L-cysteine 1-methylester (1; 70000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-beta-cyclohexyl-L-alanine 1-methylester (2; 50000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-beta-cyan-L-phenyloalanine 1-methylester (3; 2000 times more potent than sucrose), N-[3,3-dimethylbutyl]-alpha-L-aspartyl-(1R,2S,4S)-7-methyl-2-hydroxy-4-phenylhexylamide (4; 5500 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (5; 15000 times more potent than sucrose), and N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-asaortyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (6; 15000 times more potent than sucrose). The "L-shaped" structure, which we believe to be responsible for sweet taste, is accessible to all six molecules in solution. This structure is characterized by a zwitterionic ring formed by the AH- and B-containing moieties located along the +y axis and by the hydrophobic group X pointing into the +x axis. Extended conformations with the AH- and B-containing moieties along the +y axis and the hydrophobic group X pointing into the -y axis were observed for all six sweeteners. For compound 5, the crystal-state conformation was also determined by an X-ray diffraction study. The result indicates that compound 5 adopts an L-shaped structure even in the crystalline state. The extraordinary potency of the N-arylalkylated or N-alkylated compounds 1-6, as compared with that of the unsubstituted aspartame-based sweet taste ligands, can be explained by the effect of a second hydrophobic binding domain in addition to interactions arising from the L-shaped structure. In our examination of the unexplored D zone of the Tinti-Nofre model, we discovered a sweet-potency-enhancing effect of arylalkyl substitution on dipeptide ligands, which reveals the importance of hydrophobic (aromatic)-hydrophobic (aromatic) interactions in maintaining high potency.

Astins, antitumour cyclic pentapeptides, were isolated from the Aster tataricus. Their chemical structures, consist of a 16-membered ring system containing a unique β,γ-dichlorinated proline [Pro(Cl 2], other non-coded amino acid residues and a cis conformation in one of the peptide bonds. The astin backbone conformation, along with the cis peptide bond in which the β,γ-dichlorinated proline residue is involved, was considered to play an important role in their antineoplastic activities on sarcoma 180A and P388 lymphocytic leukaemia in mice, but the scope and potential applications of this activity remain unclear. With the aim at improving our knowledge of the conformational properties influencing the bioactivity in this class of compounds, new astin-related cyclopeptides were synthesized differing from the natural products by the presence of some non-proteinogenic amino acid residues: Aib, Abu, -(S)β3-hPhe and a peptide bond surrogate (-SO2-NH-). The analogues prepared c(-Pro-Thr-Aib-β3-Phe-Abu-), c[Pro-Thr-Aib-(S β3-hPhe-Abu], c[Pro-Abu-Ser-(S β3-hPheΨ(CH2-SO2-NH)-Abu] and c[Pro-Thr-Aib-(S β3-hPheΨ(CH2-SO2-NH)-Abu] were synthesized by classical methods in solution and tested for their antitumour effect. These molecules were studied by crystal-state x-ray diffraction analysis and/or solution NMR and MD techniques. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.

A comparative study has been performed on five native laccases purified from the three basidiomycete fungi Pleurotus ostreatus, Rigidoporus lignosus, and Trametes trogii to relate their different catalytic capacities to their structural properties. Spectroscopic absorption features and EPR spectra at various pH values of the five enzymes are very similar and typical of the blue oxidases. The analysis of the dependence of kinetic parameters on pH suggested that a histidine residue is involved in the binding of nonphenolic substrates, whereas both a histidine and an acidic residue may be involved in the binding of phenolic compounds. His and an Asp residue are indeed found at the bottom of a cavity which may be regarded as a suitable substrate channel for approaching to type 1 copper in the 3D homology models of the two laccases from Pleuorotus ostreatus (POXC and POXAlb) whose sequences are known.

The crystal chemistry of wavellite from Zbirov (Czech Republic), ideally Al3(PO4)2(OH,F)3·5H2O, was addressed by means of a multi-methodological approach based on electron microprobe analysis (EMPA) using wave-dispersive spectroscopy, single-crystal X-ray diffraction, powder and singlecrystal infrared spectroscopy and Raman spectroscopy. The EMPA data showed the presence of significant F replacing OH in the sample studied. The structure was solved in thePcmnorthorhombic space group, with the following unit-cell constants:a= 9.6422(7),b= 17.4146(15),c= 7.0094(2) Å,V= 1176.98(10) Å3. Phosphorus atoms display tetrahedral (PO4) coordination, while Al cations display octahedral coordination. The mineral framework can be viewed as the repetition of cationic arrays made up of AlO6polyhedra, bridged by PO4groups and further joined by O–H⋯O hydrogen bonds. The single-crystal unpolarized Fourier transform infrared (FTIR) spectrum shows combination bands indicating the presence of both OH and H2O in the structure. Both FTIR and Raman spectra show a broad absorption extending from 3600 to 2800 cm−1resulting from the overlapping of several components due to the water molecules and the OH group. The frequencies observed are comparable to those expected on the basis of the Libowitzky relationship for the range ofD–H⋯Abond systems in the structure.

The conformational behavior in solution of a cyclic peptide with sequence cyclo(Pro'-Pro2-Dab3(cHexA)ili[N-'HCO}-Leu4

Peptide Nucleic Acids (PNAs), nucleic acid analogues showing high stability to enzyme degradation and strong affinity and specificity of binding toward DNA and RNA are widely investigated as tools to interfere in gene expression. Several studies have been focused on PNA analogues with modifications on the backbone and bases in the attempt to overcome solubility, uptake and aggregation issues. γ PNAs, PNA derivatives having a substituent in the γ position of the backbone show interesting properties in terms of secondary structure and affinity of binding toward complementary nucleic acids. In this paper we illustrate our results obtained on new analogues, bearing a sulphate in the γ position of the backbone, developed to be more DNA-like in terms of polarity and charge. The synthesis of monomers and oligomers is described. NMR studies on the conformational properties of monomers and studies on the secondary structure of single strands and triplexes are reported. Furthermore the hybrid stability and the effect of mismatches on the stability have also been investigated. Finally, the ability of the new analogue to work as antigene, interfering with the transcription of the ErbB2 gene on a human cell line overexpressing ErbB2 (SKBR3), assessed by FACS and qPCR, is described. © 2012 Avitabile et al.

One of the clinical features of cystic fibrosis (CF) is a deep inflammatory process, which is characterized by production and release of cytokines and chemokines, among which interleukin 8 (IL-8) represents one of the most important. Accordingly, there is a growing interest in developing therapies against CF to reduce the excessive inflammatory response in the airways of CF patients. Since transcription factor NF-kappaB plays a critical role in IL-8 expression, the transcription factor decoy (TFD) strategy might be of interest. In order to demonstrate that TFD against NF-kappaB interferes with the NF-kappaB pathway we proved, by chromatin immunoprecipitation (ChIP) that treatment with TFD oligodeoxyribonucleotides of cystic fibrosis IB3–1 cells infected with Pseudomonas aeruginosa leads to a decrease occupancy of the Il-8 gene promoter by NF-kappaB factors. In order to develop more stable therapeutic molecules, peptide nucleic acids (PNAs) based agents were considered. In this respect PNA-DNA-PNA (PDP) chimeras are molecules of great interest from several points of view: (1) they can be complexed with liposomes and microspheres; (2) they are resistant to DNases, serum and cytoplasmic extracts; (3) they are potent decoy molecules. By using electrophoretic mobility shift assay and RT-PCR analysis we have demonstrated that (1) the effects of PDP/PDP NF-kappaB decoy chimera on accumulation of pro-inflammatory mRNAs in P.aeruginosa infected IB3–1 cells reproduce that of decoy oligonucleotides; in particular (2) the PDP/PDP chimera is a strong inhibitor of IL-8 gene expression; (3) the effect of PDP/PDP chimeras, unlike those of ODN-based decoys, are observed even in the absence of protection with lipofectamine. These informations are of great impact, in our opinion, for the development of stable molecules to be used in non-viral gene therapy of cystic fibrosis.

The complex [Cl(Ph3P)Pt(H-Aib-O)], where Ph3P and H-Aib-O are triphenylphosphine and α-aminoisobutyrate, respectively, has been synthesized and characterized in the solid state by X-ray diffraction analysis. It crystallizes as a monohydrate in the triclinic system, space group P with a=9.020, b=10.011, c=13.748 Å, α=91.74, β=90.29, γ=111.26° and Z=2 molecules per unit cell. The crystal structure has been solved by the Patterson technique and refined to a final R factor of 0.038 for the 3826 observed reflections with I≥3.0σ(I). The Pt(II) atom displays the square planar coordination with the H-Aib-O− amino acid acting as a bidentate ligand. The N atom of the H-Aib-O− residue in trans position with respect to the P atom of the triphenylphosphine moiety and correspondingly the O atom of the carboxylate is trans to the chlorine atom. The observed distortions in the bond angles around the Pt(II) atom as well as the conformation assumed by the triphenylphosphine and the H-Aib-O− residue can be all explained on the basis of the need to release the intramolecular non-bonded interactions between atoms of the various ligands. Three intermolecular hydrogen bonds, involving as donors the cocrystallized water molecule and the two hydrogen atoms of the NH groups and as acceptors the chlorine, the oxygen of the water molecule, and one of the oxygen atoms of the carboxylic acid group, together with van der Waals interactions between hydrophobic groups held the molecules in the crystal state.

The ability of PNA to interact with DNA double stranded has been recently investigated. In a decoy approach these interactions are of great importance as may lead to inhibition of interactions of DNA sequences to specific transcription factors and may be employed as a strategy for the inhibition of gene transcription alternative to the antisense strategy (targeting transcription factors mRNAs) and the transcription factor decoy approach (targeting transcription factors). We explored the ability of PNA and PNAs with modified monomers to bind to DNA and to interfere in the formation of DNA/transcription factor complex. We report a procedure for the synthesis of Fmoc-γ-hydroxymetyl PNA, the synthesis and CD analysis of PNA oligomers containing the modified monomer in different positions and EMSA assays to test the: (a) binding to double stranded DNA and (b) inhibition of DNA-protein interactions. © 2010 Elsevier Inc. All rights reserved.

The trans-[Cl2-Pt-(H-Aib-OH)2] and trans-[Pt-(H-Aib-O−)2] complexes have been synthesized and characterized in solution and in the solid state. Their crystal and molecular structures have been determined by X-ray diffraction analyses. The complexes show a distorted planar coordination around the heavy atom. The organic moiety in the two complexes shows different conformations: in trans-[Pt-(H-Aib-O−)2] the amino acid residue, acting as a bidentate, is forced to assume an unusual conformation. On the other hand, in trans-[Cl2-Pt-(H-Aib-OH)2], in which the amino acid acts as a monodentate ligand, the α-aminoisobutyric acid assumes an extended conformation, which in general for α-monosubstituted amino acid residues coordinated to the platinum should be the preferred conformation. In both crystal structures hydrogen bonds are formed between the donor and acceptor groups with further stabilization deriving from van der Waals interactions between hydrophobic moieties.

Peptide contg. a cyclic RGD motif and two echistatin C-terminal moieties covalently linked by a spacer having the following formula: AA1-Arg-Gly-Asp-AA2-(Xaa)n-L-(Yaa)m [AA1 and AA2 = a-amino acid contg. at least three functional groups, selected from Cys, Asp, Glu, Lys, Orn, Pen, Dab or Dab; L = linker sequence consisting of 0 - 2 amino acid residues from; (Xaa)n = amino acid sequence in which n = 1 - 3 , which sequence is substantially homolog to that of 28-30 of echistatin: MDD; (Yaa)m = amino acid sequence in which m = 2 - 9, which sequence is substantially homolog to that of C-terminus (41-49) of echistatin: RNPHKGPAT] were prepd. as selective avb3 integrin antagonists for therapeutic and diagnostic applications. All peptides were prepd. by solid phase peptide synthesis using Fmoc (Fmoc = 9-fluorenylmethoxycarbonyl) strategy and were tested for their ability to inhibit cell adhesion to vitronectin.

A library of 14 cyclic peptide analogues derived from the octapeptide C-terminal sequence of the human cholecystokinin hormone (CCK(26-33), or CCK8) was designed, synthesized, and characterized. The 14 peptide analogues were rationally designed to specifically interact with the CCK type B receptor (CCK(B)-R) on the basis of the structure of the bimolecular complex between CCK8 and the third extracellular loop of CCK(B)-R, namely CCK(B)-R(352-379). The rational design of new ligands for CCK(B)-R has relied on stabilization by cyclic constraints of the structural motifs that bring the key residues of the ligand (especially Trp 30, Met 31, and Phe 33) in the proper spatial orientation for optimal interaction with the receptor. The binding affinity of the new ligands for CCK(B)-R was assessed by displacement experiments of (111)In-radiolabeled CCK8 in cells that overexpress the CCK(B) receptor. The new ligands generally showed binding affinities lower than that of parent CCK8, with the best compounds having IC50 values around 10 microM. Structure-activity relationship data show that preservation of the Trp 30-Met 31 motif is essential and that the Phe 33 side chain must be present. NMR conformational studies of the compound with maximal binding affinity (cyclo-B11, IC50=11 microM) in DPC micelles shows that this compound presents a turn-like conformation centered at the Trp 30-Met 31 segment, as planned by rational design. Such a conformation is stabilized by its interaction with the micelle rather than by the cyclic constraint.

The interaction between the 1-47 N-terminus of the CCK(1)-R and the anthranilic acid based antagonists has been investigated by fluorescence spectroscopy. These antagonists interact with W39 of the N-terminal domain of the CCK(1)-R like that of the endogenous ligand CCK-8. This specific interaction was not found in other nonpeptide ligands of the CCK(1)-R. Conformational studies, using NMR and energy minimization procedures, have allowed formulation of a new hypothesis on the CCK(1)-R binding mode of the anthranilic antagonists.

In this chapter are reviewed peptide conjugates as tools in diagnostic nuclear medicine.

b-Cyclodextrins (b-CD) have received considerable attention for their suitability to serve as relatively low molecular weight models for drug delivery and for artificial enzymes. In fact, b -CD shows remarkable ability to form inclusion complexes with various natural and synthetic molecules that fit inside the b -CD cavity. The inclusion process is influenced by the interaction between the guest molecules and the cavity, and also by the shape and size of the guest. This process can change the chemical and physical properties of the guest. In particular, pharmacological properties, such as stability, solubility, and toxicity, can be improved. Then, the rational design of functionalized b -CDs with bioactive moieties can represent an important step for the development of new drugs. In this work, we report a detailed conformational analysis at atomic resolution by x-ray diffraction data and computational techniques on several functionalized b-CDs to understand the structural requirement to modulate the binding properties and basic phenomena governing the inclusion process for b-CDs.

Peptide nucleic acids (PNAs)-DNA chimeras have been recently described as DNA mimics constituted of a part of PNA and of a part of DNA. We have demonstrated that double stranded molecules based on PNA-DNA chimeras bind to transcription factors in a sequence-dependent manner. Accordingly, these molecules can be used for transcription factor decoy (TFD) pharmacotherapy. Effects of double stranded PNA-DNA chimeras targeting NF-kappaB and Sp1 were determined on in vitro cultured human cells and were found to be comparable to those observed using double-stranded DNA decoys. The TFD molecules based on PNA-DNA chimeras can be further engineered by addition of short peptides facilitating cell penetration and nuclear localization. Therefore, these engineered molecules could be of great interest for in vivo experiments for non-viral gene therapy of a variety of diseases, including neoplastic and viral diseases, for which the TFD approach has been already demonstrated as a very useful strategy.

We report a crystallographic and computational analysis of two mutant forms of the Alicyclobacillus acidocaldarius thioredoxin (BacTrx) done in order to evaluate the contribution of two specific amino acids to the thermostability of BacTrx. Our results suggest that the thermostability of BacTrx may be modulated by mutations affecting the overall electrostatic energy of the protein.

The cyclopentapeptides of the astin family contain several uncoded amino acids, namely (-)-(3S,4R)-dichloroproline, β3-homo-phenylalanine, α-aminobutyric acid (Abu), and allo-threonine. The astins, isolated from the plant roots Aster tataricus, exhibit antitumor activity (Sarcoma 180 A), but the potential applications of this biological behaviour remain to be further investigated. Conformational studies of astin A, B and C were carried out by a combination of X-ray, NMR and computational techniques [1]. The results indicate that the backbone conformation of astin A and C., with lower activity, is different from that of astin B. Therefore, both the backbone conformation and a cis linkage shown by the 3,4-dichlorinated proline residue, were considered to play an important role in the antitumor activity of these molecules [2]. The development of efficient synthetic procedures for preparation of β3-H residues and of cis-3,4-dihydroxyproline, as well as (-)-(3S,4R)-dichloroproline [3], has brought new interest in the structure-activity relationships of astin analogs. With the aim to further understand the structural and conformational requirements for activity and possibly the mechanism of action of these molecules, we have focused our attention on several cyclic pentapeptide related to astin G [4], which presents in its 16-membered ring the sequence Pro-allo-Thr-Ser-β3-HPhe-Abu. The structural results of two synthetic astin G related cyclopentapeptides c-(Pro-Thr-Aib-β3-HPhe-Abu) (I) and c-(Pro-Thr-Aib-β3-HPhg-Abu) (II) are reported.

Oligonucleotides carrying a peptide nucleic acid (PNA) tail at the 3′-end have been efficiently prepared by an on-line automated synthetic protocol exploiting commercially available Bhoc/Fmoc PNA monomers for the assembly of the PNA tract, followed by a deprotection/reprotection of the base protecting groups. The syntheses of the ODN domain in the chimeras have then been performed by standard methods. The hybridization properties of the synthesized chimeras with complementary DNA fragments have been investigated by thermal denaturation experiments. © 2001 Elsevier Science Ltd. All rights reserved.

A bicyclic undecapeptide of sequence cyclo-(Ala(1)-Pro(2)-Asp(3)-Glu(4)-Lys(5)-Ala(6)-Pro(7)-Asp(8)-Ser(9) -Glu(10))-cyclo-(10gamma --> 5varepsilon)-Gly(11), designed to mimic the calcium coordination site I of Calmodulin, has been synthesized and its conformation and calcium binding properties have been investigated by means of CD and nmr spectroscopy. The nmr analysis of the free peptide, carried out in DMSO and in TFE/H(2)O at different pH values, shows the presence in solution of one stable conformer, exhibiting trans configuration around both Proline residues. The nmr results in both solvents suggest for the molecule a rectangular shape constituted by two antiparallel beta-strands connected by two beta-turns. Interproton distances, evaluated by NOE contacts, have been used to obtain feasible models by means of Restrained Molecular Dynamic (RMD). The average models from RMD calculations, for both solvents, exhibit good analogies with Calmodulin site I. The model system, when compared with the reference system (Asp(20)-Glu(31) segment in CaM), shows similar dimensions and an effective superimposition of the respective sequence segments Ala(1)-Glu(4) and Thr(28)-Glu(31). The remaining segments of the model peptide exhibit a bending that is intermediate between that of the free and Ca(2+)-coordinated site I. CD spectra, recorded in TFE solutions, point to a 1:1 stoichiometry for the Ca(2+)-peptide complex, with an association constant of at least 1 x 10(5) M(-1).

6I,6II-Diamino-6I,6II-dideoxy-cyclomaltoheptaose was prepared using the regioselective procedure described by Tabushi. The difunctionalized β-cyclodextrin crystallizes as hexadecahydrate in the orthorhombic space group P212121, with a = 11.395(3), b = 32.989(9), c = 17.560(5) A , V = 6601 A 3 , Z = 4 . The structure was solved by molecular replacement techniques using the program PATSEE and was refined to a conventional final R = 0.058 for the 5031 observed reflections with I ⩾ 3σ(I). The β-CD macrocycle presents only slight differences with respect to uncomplexed hydrated or methylated β-CD. The macrocycle structure maintains an approximate seven-fold symmetry. The round shape of the cyclodextrin ring is stabilized by intramolecular OH … O H-bonds between the secondary hydroxyl groups of neighbouring glucose residues. Along the a axis, the β-CD molecules are arranged in columns; the macrocycles form a herring-bone pattern, so that the cavity of each β-CD molecule is closed at each end by neighbouring molecules. The macrocycles are directly linked to each other by H-bonds involving either primary and secondary hydroxyl or amino groups of symmetry-related molecules. The resulting layers are connected to each other by a dense intermolecular hydrogen-bond network, in which solvent molecules participate.

Irregular protein secondary structures are believed to be important structural domains involved in molecular recognition processes between proteins, in interactions between peptide substrates and receptors, and in protein folding. In these respects tight turns are being studied in detail. They also represent template structures for the design of new molecules such as drugs, pesticides, or antigens. Isolated α-turns, not participating in α-helical structures, have received little attention due to the overwhelming presence of other types of tight turns in peptide and protein structures. The growing number of protein X-ray structures allowed us to undertake a systematic search into the Protein Data Bank of this uncharacterized protein secondary structure. A classification of isolated α-turns into different types, based on conformational similarity, is reported here. A preliminary analysis on the occurrence of some particular amino acids in certain positions of the turned structure is also presented. © 1996 John Wiley & Sons, Inc.

A monofunctionalized β-cyclodextrin containing a dansyl moiety, 6- deoxy- 6 - N - ( N′- (5- dimethylamino - 1 - naphthalenesulfonyl)diaminoethane) - β-cyclodextrin (CD-en-DNS, 2), was synthesized and its crystal structure determined. It was shown that the dansyl group is fully encapsulated within the cyclodextrin cavity, with the dimethylamino and sulfonyl groups emerging from opposite sides. The shape of the cavity is considerably flattened, since O(4)–O(4) distances parallel to the naphtalene ring were found to be longer than the others. The conformation of the diaminoethane linker was found to be determined by the inclusion of the dansyl group and by a hydrogen bond between the sulfonamide NH and one of the O(6)–H groups on the cyclodextrin rim. The self-inclusion features of the aromatic moiety were found to be consistent with the solution data: 1H NMR ROESY spectra suggested that the orientation of the dansyl moiety observed in the solid state was retained in aqueous solution; the circular dichroism spectrum was consistent with an axial complexation model. Fluorescence spectra showed that the inclusion of the dansyl group in the cyclodextrin cavity considerably increases the quantum yield: time-resolved fluorescence experiments showed the presence of a long-lifetime component (16.1 ns), which was attributed to the included fluorophore. The ability of 2 to act as a fluorescence sensor was evaluated by the addition of several guests of different shape: fluorescence intensity was lowered, especially upon addition of adamantanecarboxylic acid. All the data obtained were consistent with the model of the in-out movement of the dansyl group from the self-included conformation observed in the solid state to a position more exposed to the bulk solvent. Copper(II) was shown to enhance the difference in the fluorescence of 2 in the presence of guests by additional static quenching.

In the present paper we describe the synthesis, purification, and single crystal x-ray analysis of the cyclic pentapeptide cyclo-(Pro-Phe-Phe-β-Ala-β-Ala). This compound crystallizes in the orthorhombic space group P212121 from methanol and adopts in the solid state an unusual conformation characterized by a cis β-Ala5-Pro1 peptide bond and by an intramolecular hydrogen bond stabilizing a C11- and a C12-ring structure. The C11, structure contains the Phe3 and the β-Ala4 at the corner position of the turn; it is the first observation of a type II β-turn enlargement due to the insertion of an extra methylene group of the β-alanine residue. The rest of the molecule participates in a newly characterized C12-ring structure, which incorporates a β-Ala residue at position i of the turn. © 1996 John Wiley & Sons, Inc.

Synthetic peptides reproducing the proteolytic processing site of pro-ocytocin were studied by different spectroscopic techniques, including circular dichroism, Fourier transform infrared absorption, and mono and bidimensional nuclear magnetic resonance, in order to ascertain the possible role of three-dimensional structure in the recognition process by maturation enzymes. Experimental results were compared with energy minimization calculations and suggest that: (i) the region situated on the N-terminus of the Lys-Arg doublet may form a beta-turn; (ii) the sequential organization of the residues participating in the beta-turn determines the privileged relative orientation of the basic amino acid sidechains and the subtype of turn; and (iii) the peptide segment situated on the C-terminal side of the dibasic doublet may assume a helix arrangement. These findings, in spite of the limitations connected to the flexibility of linear peptides, seem to substantiate the hypothesis that structural motifs around the cleavage site could be important for recognition and processing. however, a straightforward correlation between details of the secondary structure and the in vitro reactivity toward a putative convertase is not yet possible.

A single‐crystal x‐ray diffraction analysis of Boc‐L‐Ala‐D‐aIle‐L‐Ile‐OMe has been carried out. The analysis has shown (a) that the tripeptide molecules have in part an α‐extended conformation, the torsion angles of the L‐Ala and D‐aIle residues being φ1 = −75.1° and ψ1 = −25.8° and φ2 = 67.3° and ψ2 = 44.1°, respectively, and (b) that the molecules are organized in rippled planes where they occur in relative antiparallel orientation linked together side by side by H bonds. This molecular organization of the tripeptide corresponds closely to that of an antiparallel α‐pleated sheet, and likely constitutes the first example of a structure of this kind for which a characterization at the atomic level has been achieved. A molecular dynamics study has shown that the molecular conformation of the tripeptide in the crystalline state is determined primarily by intermolecular interactions. © 1994 John Wiley & Sons, Inc. Copyright © 1994 John Wiley & Sons, Inc.

The title compound, L-Prolyl-L-leucyl-L-prolinamide, C 16 H 28 N 4 O 3 , is folded at the N-terminal L-Pro residue and semi-extended at the central L-Leu and C-terminal L-Pro residues. The L-Leu side chain is in the common g - (t,g - ) disposition

A complete structural characterization in solution, by NMR spectroscopy, and in vacuo, by molecular dynamic simulations, of two synthetic peptide fragments from SBBI (Soybean Bowman–Birk Inhibitor) is reported. Peptide 197, corresponding to the SBBI(41–49) chymotrypsin recognition site, has free N- and C-terminal groups, while peptide 212, corresponding to the Leu 16-SBBI(14–22) has uncharged and fully protected terminal ends. Peptide 212 shows significant anti-chymotryptic activity while peptide 197 is inactive. Neither of the two peptides shows anti-tryptic activity. The structural information obtained in the present paper suggests a quantitative structure–activity relationship which may help both in understanding the mechanism of action of protease inhibitors, and in providing new directions for the rational design of more specific and potent inhibitors.

Bioactivation of pro-proteins by limited proteolysis is a general mechanism in the biosynthesis of hormones, receptors and viral protein precursors. This proceeds by cleavage of peptide bonds at the level of single or pairs of basic residues in the proforms. Examination of a number of cleavage loci in various precursors failed to reveal any consensus primary sequence around the dibasic cleavage sites. Thus it has been proposed, on the basis of secondary structure predictions [Rholam, M., Nicolas, P. and Cohen, P. (1986) FEBS Lett., 207, 1-6], that those basic residues which operate as signal loci for the proteolytic enzyme machinery are situated in, or next to, privileged precursor regions most often constituted by flexible and exposed motifs, e.g. beta-turns and/or loops. Peptides reproducing the N-terminal processing domain of the hormone precursor, pro-ocytocin-neurophysin, were examined by a combination of spectroscopical techniques including circular dichroism, infrared Fourier transform and one- and two-dimensional proton NMR. The results indicate that: (i) the region situated on the N terminus of the Lys-Arg doublet is organized as a beta-turn in solution; (ii) the sequential organization of the residues participating in the beta-turn determines the privileged relative orientation of the basic amino acid side chains and the subtype of turn; (iii) the peptide segment situated on the C-terminal side of the dibasic, corresponding to the N-terminal octapeptide of neurophysin, is organized as an alpha-helix.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular and crystal structure of two terminally blocked (L-Pro-Aib) n (n=3,4) sequential peptides were determined by X-ray diffraction. In both crystals two molecules in the asymmetric unit are found. Either molecule in the asymmetric unit of each structure shows a right-handed β-bend ribbon spiral, stabilized by the maximum possible number of intramolecular N-H...O=C H-bonds. Thus, for the first time it was possible to characterize at atomic resolution this polypeptide conformation

The new platinum(II) complex of 6A,6B-diamino-6A,6B-dideoxycyclomaltoheptaose was synthesized and characterized by spectroscopy (NMR, FAB MS, UV, c.d.) and X-ray diffraction analysis. The complex crystallizes in the ortorhombic space group P212121 with a = 26.970(2), b = 15.102(2), and c = 16.142(2) Å. The Pt(II) has a square-planar coordination with two chlorine atoms and two amino groups in a cis disposition. The complexation with the Pt(II) induces a distortion of the cavity. The hydrogen bonds on the secondary hydroxyl groups, which involve the functionalized rings, are longer and consequently weaker than the other hydrogen bonds.

We have recently undertaken a systematic structural analysis of fully protected tetrapeptides containing at the N- and C-terminus either homo- or heterochiral amino acids, spaced by an achiral dipeptide segment. The interest for this class of peptides derives from the observation that, on reverse-phase (HPLC), the homo- and heterochiral sequences have a markedly different retention times. The diastereomeric sequences, namely Z-(L/D)-Val-X-Y-L-Phe-OMe (X = Sar, Gly, Ac3c, Aib, Ac5c, Ac6c, Deg, Dpg, Dbu, Dip, Dph; Y = Sar, Gly, Ac3c, Aib, Ac5c, Ac6c) show different overall hydrophobicity attributed to a different three-dimensional structure that also depends on the X-Y segment. Therefore, following preliminary studies in solution, we report here the detailed x-ray analysis of the tetrapeptide Z-D-Val-Ac6c-Gly-L-Phe-OMe in order to understand the structural features governing the overall hydrophobicity of linear fully protected tetrapeptides.

An N- and C-protected derivative of homo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates an extended conformation for this homo-β-residue, with the φ torsion angle being more constrained than the μ and ψ angles.

PNAs conjugated to carrier peptides have been employed for the targeting of miRNA precursor, with the aim to develop molecules able to interfere in the pre-miRNA processing. The capability of the molecules to bind pre-miRNA has been tested in vitro by fluorescence assayes on Thiazole Orange labeled molecules and in vivo, in K562 cells, evaluating the amount of miRNA produced after treatment of cells with two amounts of PNAs.

We report the detailed X-ray structure of the fully blocked tetrapeptide Z-D-Val-(Aib)2-L-Phe-OMe. The compound crystallizes in the space group P21 with four independent tetrapeptide molecules aligned in a parallel arrangement along the c axis. There is a regular alternation of right- and left-handed 310-helices hydrogen bonded head-to-tail along this axis. Pairs of molecules with the same handedness differ in the conformation of the side chains and of the N- and C-terminal blocking groups. This is the first observation, to the best of our knowledge, of a helical peptide containing chiral α-monosubstituted α-amino acids without a preferred screw sense. Conformational energy computations confirmed that those helices with different handedness have comparable stabilities. This work is a part of our studies on fully protected tetrapeptides containing homo and hetero chiral residues at N- and C-termini spaced by an achiral dipeptide segment, in order to understand the structural features responsible for the diastereoselective separation by reversed-phase HPLC.

The combined use of several nuclear magnetic resonance and restrained molecular dynamics techniques allowed the formulation of a molecular model for the preferred solution conformation of a synthetic peptide reproducing the [1-20] processing domain of the pro-ocytocin-neurophysin precursor. In the model, the conformation of the 20-membered tocin ring, with the two Cys1 and Cys6 residues bridged by a disulphide bond, is very close to that observed for isolated ocytocin in the solid state; in addition, a type II β-turn is postulated for the 7-10 segment of the acyclic tail containing the Lys11-Arg12 processing site, and connecting ocytocin to the neurophysin domain, while the C-terminal 13-20 segment of the molecule is believed to assume a helical structure. This particular structural organization could be important in participating as the favorable conformation for optimal substrate-enzyme active site recognition and processing by specific endoproteases. © 1996 John Wiley & Sons, Inc.