摘要:

The solid‐state structure of a heterochiral peptide embodying a D‐aminosuccinyl peptide (D‐ASU) and a D‐Ala was studied in order to analyse the effects of Asu and amino acids with inverse chirality on peptide conformation. The crystal structure has been determined by X‐ray diffraction techniques and refined to a finalRfactor of 0.043. The molecule adopts an unusual overall 'S‐shape’ conformation due to two consecutive type II β‐turns. In this molecule it is possible to compare a type II β‐bend conformation (L‐Ala1‐D‐Ala2) favoured by the presence of a D‐residue at second corner to a type II β‐turn (D‐Asu3‐Gly4) favoured by the presence of a D‐ASU residue at first corner. In agreement with previous studies, this structure confirms that the Asu has a high propensity to adopt a type II or II′β‐bend conformation and that it may be used as a strong determinant of t

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01349.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The molecular and crystal structures of one derivative and two oligopeptides of TOAC, a nitroxide spin‐labelled Cαα‐disubstituted glycine, have been determined by X‐ray diffraction. The derivative is the 5(4H)‐oxazolone from Piv‐TOAC‐OH; the oligopeptides are Z‐TOAC‐(L‐Ala)2‐NHtBu sesquihydrate andpBrBz‐TOAC‐(L‐Ala)2‐TOAC‐L‐Ala‐NHtBu hemihydrate. Incipient and fully developed right‐handed 310‐helical conformations are formed by both independent molecules in the asymmetric unit of the terminally blocked tripeptide amide and the terminally blocked pentapeptide amide, respectively. The average geometry and preferred conformation for the piperidine ring of the TOAC residues are also

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01350.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

An efficient Metropolis Monte‐Carlo (MMC) procedure is proposed in order to calculate averages of the energy of conformation and structural properties of a polypeptide chain in interaction with a solvent. The contribution of hydration to the free energy of conformation of the macromolecule is calculated using the accessible surface area method. This algorithm, performed with different sets of atomic solvation parameters (ASP), is applied to the peptidic hormone angiotensin II. Different situations of solvation of that molecule are described when the ASP of the polar atoms are fixed to 0, whereas those of the apolar atoms are given values varying from ‐1.0 to 1.0. From results thus obtained, transitions from extended to collapsed conformations of the polypeptide chain can be simulated. Such changes of conformation could be related to a possible mechanism of binding of this hormone on a membrane surface. © Munksgaard

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01351.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We introduce solid‐phase syntheses of H‐ and methylphosphonopeptides, giving access for the first time to a new class of mimics foro‐phosphoamino acids. The model peptides H‐GlyGlyXaaAla‐OH (Xaa = Ser, Thr) were synthesized on a solid‐phase using Fmoc/tBu strategy and HBTU/HOBt activation by incorporation of hydroxyl‐protected serine and threonine. As selectively cleavable hydroxyl‐protecting groups we used triphenylmethyl andtert‐butyldimethylsilyl for both amino acids, as described in the literature. All peptides were phosphitilated withO,O‐di‐tert‐butyl‐N,N‐diethylphosphoramidite and yielded H‐phosphonopeptides after trifluoroacetic acid cleavage. Alternatively we phosphonylated the peptides withO‐tert‐butyl‐N,N‐diethyl‐P‐methylphosphonamidite, which was synthesized by a two‐step one‐pot procedure starting from commercially available chemicals. All H‐ and methylphosphonopeptides were obtained in high purities and yields, as shown by reversed‐phase high‐performance liquid chromatography and anion‐exchange chromatography.The phosphonopeptides were characterized by1H and31P NMR. We confirmed their molecular masses by electrospray mass spectrometry and analyzed their fragmentation schemes, which seemed to be characteristic for each class of analogues. The H‐phosphonopeptides lost phosphonic acid (H3PO3, 82 mass units) and the methylphosphonopeptides lost methylphosphonic acid (MeH2PO3, 96 mass units). Both H‐ and methylphosphonopeptides represent a new and simply accessible class of mimics for phosphopeptides. Compared with the corresponding phosphopeptides all phosphonopeptides were synthesize

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01352.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Legumin‐T, the high‐molecular mass product of limited tryptic hydrolysis of faba bean legumin, was investigated using hydrodynamic methods, static light scattering, fluorescence and ultraviolet spectroscopy. The following physico‐chemical parameters were determined in a high‐ionic strength buffer system: molecular mass, 2.4 × 105g/mol; sedimentation coefficient,s310= 10.8 × 10−13si; diffusion coefficient,D020= 4.1 × 10−7cm2s−1; intrinsic viscosity, [n] = 3.51 mL/g; partial specific volume, v∣⃝= O.719 mL/g; frictional ratio,f/fo= 1.22; shape factor, β= 2.17 × 106. Conformational changes during the formation of legumin‐T can be deduced from the fluorescence emission and UV s

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01353.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Peptides representing single repeat units of the carboxy‐terminal domain (CTD) of RNA polymerase II (Tyr‐Ser‐Pro‐Thr‐Ser‐Pro‐Ser‐Tyr‐NH2, 1) contain overlapping Ser‐Pro‐Xaa‐Xaa β‐turn forming sites which permit their overall structure to closely resemble members of the quinoxaline class of antitumor DNA bisintercalators. We have modified this native sequence at thei+2positions of each β‐turn unit by substituting Gly or D‐Ala in an attempt to preorganize this structure in aqueous solution. CD and NMR spectroscopic investigations confirmed the presence of type II β‐turns within each of the substituted peptides in contrast to the native sequence which contains a relatively low population of turn structure. In addition, an examination of singly substituted peptides suggests that an increase in the population of β‐turn structure within the amino‐terminal Ser‐Pro‐Xaa‐Xaa site also increased the formation of β‐turn structure in the carboxy‐terminal (unmodified) Ser‐Pro‐Xaa‐Xaa site; in comparison, substitution in the carboxy‐terminal site did not influence structure in the remaining portion of the peptide. Overall, these results suggest that the structures formed could provide unique. preorganized linkers for the construction of

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01354.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The use of chitin as a support for solid‐phase peptide synthesis is described and illustrated by synthesis of four peptides, varying in length from 10 to 29 residues. Syntheses were performed in a continuous‐flow peptide synthesizer, using Fmoc chemistry. A cleavable linker,p‐[(R,S)‐α‐[1‐(9H‐fluoren‐9‐y1)‐methoxyformamido]‐2,4‐dimethoxybenzyl]‐phenoxyacetic acid, was attached to chitosan at the desired substitution level, and the complex acetylated to yield a linker substituted chitin. The effects of temperature, solvents and degree of linker substitution on the syntheses were studied. Acyl carrier peptide (ACP) synthesis studies indicated that temperature was the single most important parameter. Increasing the temperature of the synthesis from 20 to 55 °C resulted in an enormous improvement of this synthesis, with about 90% of the crude product being the correct peptide. Denaturing solvents, such as DMSO, could be used without significant effect on the flow properties of the support. The synthesis of one peptide was mainly improved by lowering the degree of substitution from 0.3 to 0.1 mmol/g, suggesting peptide aggregation was a problem in this case. The results of three syntheses on chitin were comparable with those obtained with a commonly used commercial support. This work shows that, under appropriate conditions, chitin can be utilized directly as a support for peptide s

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01355.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Through a kinetic study of the reaction of phosphoamino acids as incubated in alcohol, it was found that the inter‐ and intramolecular phosphoryl transfer reactions were regiospecific and stereoselective. First, the phosphoryl transfer reaction required the regio‐specifically neighboring α‐carboxy group activation of amino acid but not 8‐carboxy group. The intramolecular side chain catalytic effects relative to hydrogen forN‐phosphoamino acids compared toN‐phosphoglycine were a 119‐ to 4‐times enhancement of the phosphoryl transfer reaction, respectively. Secondly, the intramolecular N→O phosphoryl transfer migration was highly stereoselective, since the reaction rate constant of phosphoallothreonine relative to its diastereomeric threonine was reduced to half. The pentacoordinate transition states modulated by the amino acid side chains were demonstrated by the formation rates of intramolecular pentacoordinate spiro mixed anhydride compounds.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01356.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

An increase in the rate of protein synthesis is found to be accompanied by phosphorylation of the 40S ribosomal protein S6. Treatment of S6 by cyanogen bromide produced three fragments, and one of the fragments of S6, which is aC‐terminal portion of S6 (Mr≅ 4000), contains all phosphorylation sites of S6. TheC‐terminal fragment of S6 contains seven serines. S6 kinase phosphorylates S6 specifically, i.e. five serines in theC‐terminal of S6 are phosphorylated. The three‐dimensional structure of S6 peptide was studied in 50% trifluoroethanol/50% H2O solution by1H NMR with combined use of distance geometry and restrained molecular dynamics calculations. NMR results indicated that it takes an α‐helix between Glu5 and Arg21 and a distorted helical structure for the following three residues, but no rigid structure was present from Ser25 through theC‐terminus and for theN‐terminal region (Lys1‐Lys4). The specificity of the phosphorylation of the peptide is discussed from a structural aspect.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01357.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The 42‐amino acid Aβ, the major constituent of the senile plaque deposits of the brains of Alzheimer's disease patients, exhibits a high degree of heterogeneity at itsN‐terminus. Isomerization of aspartic acid bonds at residues 1 and 7 renders Aβ more prone to aggregate and form extended structure as it was shown byin vivoandin vitrostudies. We recently demonstrated the ability of mid‐chain aspartic acid‐bond isomerization to break the dominant helical structure of theN‐terminal decapeptide fragment by CD. In the current study we use molecular modeling to show that insertion of the extra ‐CH2‐group into the decapeptide backbone results in the formation of stable reverse‐turns and destabilizes the helical conformer that competes with the extended structure at the full‐sized peptide level. The molecular modeling also reveals a limited propensity of the diisomerized peptide to form extended structure directly. Anti‐Aβ pAb 2332 is more sensitive for the non‐isomerized status of the decapeptide than that of the full‐sized peptide. mAb 6E10, raised against unmodified Aβ recognizes only the unmodified decapeptide or the peptide isomerized at the first aspartic acid in a conformation‐dependent manner, but does not recognize the mid‐chain isomerized or diisomerized decapeptide in any circumstance. The diisomerized decapeptide was used as immunogen to generate polyclonal antibody 14943 that is not selective for the isomerized status of either the full‐size peptide or the decapeptide, but recognizes the isomerized peptides preferentially when the peptide antigen structures are conserved during the enzyme‐linked immunoassay procedure. Owing to the aberrant behavior of the full‐sized Aβ peptide during standard RP‐HPLC, serum stability studies that indicate extracellular stability can be more effectively performed on the decapeptide fragments. Remarkably, the diisomerized peptide exhibits a significantly increased stability towards serum peptidases compared with the unmodified or monoisomerized peptides, suggesting a possible mechanism of the retention of the isomerized Aβ peptide

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb01358.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY