Critical peptide size for insolubility caused by a .BETA.-sheet aggregation and solubility improvement in hydrophobic peptides by replacement of alanine residues with .ALPHA.-aminoisobutyric acid residues.

概要

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In order to demonstrate an important role of a β-sheet aggregation on insolubility of peptides, hydrophobic peptides having partial amino acid sequences found in natural proteins have been prepared by the step-wise elongation and fragment condensation methods. In conformity with the solubility prediction for protected peptides in our previous paper, solubility data indicate that insolubility of peptides appears to begin at octa- or nonapeptide levels. In hydrophobic sequences found in proteins, the structure of peptide backbones, namely, the β-structure clearly plays an important role on insolubility of peptides, but the composition of peptides does not. Solubility improvement in hydrophobic peptides included in α-helical regions of proteins is easily achieved by replacement of Ala residues with Aib residues. High solubility of the peptides containing Aib residues is clearly explained by the observation that replacement of C<SUP>α</SUP> hydrogen atoms with methyl groups greatly disturbs β-sheet structures, promoting helical folding in peptides. The great ability of an Aib residue to promote helical folding is distinctly revealed in the peptide fragments included in α-helical regions of proteins as demonstrated before in model oligo(Leu)s.
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