Yves Trudelle

Conformational study of the sequential (Tyr-Glu)n copolymer in aqueous solution

Abstract Conformational properties of the sequential poly(Tyr-Glu) copolymer in aqueous solution were investigated as a function of pH. No transition could be detected over the range pH 13-10.5. Below pH 10.5 an aggregation process takes place, causing a drastic change in all optical properties of the polymer (optical rotation, c.d. and u.v. spectra). By means of i.r. spectroscopy in D2O, aggregates were found to be in antiparallel β conformation. The c.d. spectrum of β-aggregates is very similar to that of α-helical poly( l -tyrosine) in organic solvents, except in the 280 nm region. In addition the aggregation process is accompanied by a strong hyperchromic effect in the 277 nm absorption band. Using space-filling models, different arrangements of the chains in the β-aggregates were shown to be realizable. All result in a close stacking of tyrosyl phenyl groups, which can explain the drastic changes in all optical properties.

Conformations of gramicidin A and its 9,11,13,15-phenylalanyl analog in dimethyl sulfoxide and chloroform

In order to understand the difference in single channel behavior of gramicidin A as compared to that of gramicidin M- which is the mirror image of gramicidin M (all four tryptophanyl residues substituted by phenylalanine), conformational investigations were made under several experimental conditions. It is shown that, when examined under identical conditions, both molecules adopt the same conformations which could be identified in dimethyl sulfoxide (DMSO) and chloroform. In DMSO the conformation is based on a succession of beta-turns while in chloroform gramicidin A and M- can adopt a dimeric hybrid structure: a double helix terminated by two single-stranded helices involving the N- and C-terminal parts, respectively. It is therefore concluded that the difference in the energy profile between both gramicidins which was deduced from the ion transfer data has its origin in the nature of the aromatic side chains.

Efficient binding to the MHC class I Kd molecule of synthetic peptides in which the anchoring position 2 does not fit the consensus motif

Peptides eluted from the MHC class I Kd molecule are generally nonamers that display a strong preference for Tyr in position 2 and Ile or Len in position 9. We investigated the binding ability of several synthetic peptides which did not fit this consensus motif. In our peptides, Tyr2 was substituted by other amino acids, i.e. Len, Ile or Met. These peptides were variants of the 252–260 Kd‐restricted peptide SYIPSAEKI derived from the Plasmodium berghei circumsporozoite protein. They bound to purified Kd molecules in vitro with intermediate affinity. One of them was tested for in vivo stimulation of T cells and induced a cytotoxic response. These results demonstrate the importance of binding motif refinement to discover new binding characteristics and new ligands such as low‐affinity peptides.

Experimental and theoretical study of gramicidin P, an analog of gramicidin A with a methylamine C‐terminal

Gramicidin P (a gramicidin A in which the ethanolamine C‐terminus is replaced by methylamine) was synthesized and shown to have the same single‐channel conductance behavior as gramicidin A. The results are discussed in connection with the energy profile computed in the presence of water in comparison with the corresponding profile for gramicidin A.

Single channels and surface potential of linear gramicidins.

The single channel data for 4 different linear gramicidins containing either 4 Trp, 4 Phe, 4 Tyr or TyrBzl have been analyzed on the basis of 3 barriers-2 sites model. They form 2 families which differ by their single channel behavior and thus different energy profiles of the channel. A relationship between the surface potential and the entry barrier is proposed.

Circular dichroism study of poly(l-tyrosine), poly(l-glutamic acid) and of random and sequential copolymers of l-glutamic acid and l-tyrosine in trimethylphosphate

Abstract Random and sequential copolypeptides containing l -glutamic acid and l -tyrosine, as well as poly( l -tyrosine) and poly( l -glutamic acid) were investigated by means of c.d. spectroscopy in trimethylphosphate as solvent. In random copolymers, variation of ellipticities at 202.5 and 230 nm versus tyrosyl content follows a smooth curve, without any sharp change. This led to the conclusion that poly( l -tyrosine) α-helix is right-handed. From c.d. studies on sequential copolymers we were able to recognize that the 230 nm contribution of tyrosyl side chains is closely related to the array in which tyrosyl residues are arranged in the chain. For instance, it was found that (n, n + 2) and (n, n + 3) pairings of tyrosyl side-chains in (Tyr-Glu)n and (Glu-Tyr-Glu)n respectively, were poorly effective, while the (n, n + 4) pairing in (Glu-Glu-Tyr-Glu)n is more. However, the strongest contribution at 230 nm was observed on the alternating-pairs copolymer (Glu-Tyr-Tyr-Glu)n. This result suggests a new conformational arrangement of tyrosyl side chains in sequential copolymers, as well as in poly( l -tyrosine) and other aromatic polypeptides, based on a regular pairing of the aromatic groups, arranged in two contiguous superhelices.

Influence of the nature of the aromatic side-chain on the conductance of the channel of linear gramicidin : study of a series of 9,11,13,15-Tyr(O-protected) derivatives

This paper describes the single channel properties of a series of synthetic analogues of gramicidin A, where all four tryptophans are replaced either by tyrosine or by several O-protected (benzyl, methyl, ethyl or t-butyl) derivatives. It is shown that, although all analogues bear similar dipole moment on their side-chains, the conductance depends on the hydrophobicity of these protecting groups. An analysis of the conductance data suggests that the conductance is governed by the binding process and a possible explanation, based on conformational considerations, is proposed.

Influence of the conformation of a macromolecule on the generation of T-cell proliferative response A study with model polypeptides

To study the influence of the conformation of polypeptidic macromolecules on the generation of T‐cell epitopes, sequential polypeptides with an octamer repeat unit were designed and synthesized. They adopt mainly unordered and α‐helical conformations. Among these polypeptides, those containing proline are fully or partly unordered, and are more effective at inducing T‐cell proliferation than a proline‐free very stable α‐helical polypeptide. This extremely stable α‐helical conformation, probably stabilized by aggregation, would enhance its stability against proteolytic processing.

A new route to sequential polypeptides combining solid phase synthesis and solution peptide synthesis

Abstract The cleavage of a resin-bound peptide from an oxime resin using the 2-phenacyloxyphenyl ester of an aminoacid provides a peptide with this aminoacid in C-terminal position. The inactive 2-phenacyloxyphenyl peptide ester thus obtained can then be converted into 2-hydroxyphenyl acts active ester. The polymerization of the repeat unit using this mode of activation gives sequential polypeptides of reasonable molecular weight and of high optical purity.