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W R Fiori

Publications and source records attributed to W R Fiori.

5 recordsLinked to original sources
PubMed1995

Exploring the peptide 3(10)-helix reversible alpha-helix equilibrium with double label electron spin resonance.

Over the last several years we have used spin labeling as a means for exploring the structure of helical peptides. Two nitroxide labels are engineered into a peptide sequence and distances are ranked with electron spin resonance (ESR). We have found that there is a significant amount of 3(10)-helix in 16-residue model peptides containing only L-amino acids. This review covers several facets of the methodology including spin labeling strategy, interpretation of ESR spectra and the influence of molecular dynamics on the spectral line shapes. Also covered are recent findings of a length-dependent 3(10)-helix-->alpha-helix transition and the role of Arg+ in the stabilization of specific helix structures.

Amino Acid Sequence↗
PubMed1994

A single carboxy-terminal arginine determines the amino-terminal helix conformation of an alanine-based peptide.

Arginine is a stabilizing element in both thermophilic and low molecular weight proteins. Similarly Lys+-->Arg+ substitutions increase the helix content of designed helical peptides. Here we explore this 'arginine effect' by examining how Lys+-->Arg+ substitutions influence the 3(10)-helix-->alpha-helix equilibrium in the helical peptide Ac-(AAAAK)3A-NH2. The unsubstituted sequence contains a significant amount of 3(10)-helix, however, single Lys+-->Arg+ substitutions shift the peptide conformation toward alpha-helix in a position-dependent fashion. The single substitution closest to the carboxy terminus induces the largest conformational change at the helix amino terminus. These findings suggest that a single strategically-placed arginine can exert long range control on helix structure.

Amino Acid Sequence↗
PubMed1993

Increasing sequence length favors alpha-helix over 3(10)-helix in alanine-based peptides: evidence for a length-dependent structural transition.

Ala-based peptides form marginally stable helices at low temperature and are conventionally considered as mixtures of alpha-helix and random coil. However, recent work with doubly spin-labeled peptides suggests that short 16-residue sequences contain a significant fraction of 3(10)-helix near the N-terminus (positions 4-8). Using the same double-label strategy, we report on the helix geometry of the peptides Ac-(AAAAK)nA-NH2 with n = 3 and n = 4. The 16-mer (n = 3) is now examined at a region near the C-terminus, and there is evidence for 3(10)-helix here as well. The 21-mer (n = 4) is examined in three regions of the sequence. In dramatic contrast to the 16-mer, the 21-mer exhibits the signature of alpha-helix at the N-terminus and on through the middle of the peptide. The 21-mer C-terminus, however, adopts the 3(10)-helix geometry as is often found for C-termini in protein alpha-helices. These data indicate that the proportion of alpha-helix and 3(10)-helix in Ala-based peptides depends upon the sequence length.

Alanine↗
PubMed1992

Short alanine-based peptides may form 3(10)-helices and not alpha-helices in aqueous solution.

Short alanine peptides, containing 16 or 17 residues, appear to form alpha-helices in aqueous solution. But the main spectroscopic analyses used on helical peptides (circular dichroism and nuclear magnetic resonance) cannot distinguish between an alpha-helix (in which the ith residue is hydrogen-bonded to residue i + 4; ref. 9) and the next most common peptide helix, the 3(10)-helix10 (i-->i + 3 hydrogen-bonding). To address this problem we have designed single and doubly spin-labelled analogues of alanine-based peptides in which the nitroxide spin label forms an unbranched side chain extending from the sulphur atom of a cysteine residue. Here we report the circular dichroism, Fourier-transform infrared and electron-spin resonance spectra of these peptides under helix-forming conditions. The infrared absorbance gives an amide I' band with a frequency that is substantially different from that observed for alpha-helices. The electron-spin resonance spectra of doubly labelled helices show that the ranking of distances between side chains, around a single turn (residues 4-8), is inconsistent with an alpha-helical structure. Our experiments suggest that the more likely peptide geometry is a 3(10)-helix.

Alanine↗