α-Helix stabilization by natural and unnatural amino acids with alkyl side chains

P. C. Lyu, J. C. Sherman, A. Chen, N. R. Kallenbach

Research output: Contribution to journalArticle

Abstract

Knowledge of the role of individual side chains in forming different secondary structures such as the α-helix would be useful for prediction of protein structure from sequence or de novo protein design. Experimental and theoretical studies on natural and synthetic peptides and proteins indicate that individual side chains differ in their helix-forming potential. Four aliphatic side chains occur in the standard complement of amino acids: alanine and leucine are helix stabilizing, whereas isoleucine and valine are weakly destabilizing. We have synthesized a series of helical peptides containing unnatural aliphatic side chains having two to four carbons to explore some of the factors involved in α-helix stabilization and the basis for selection of the natural set. We find that linear side chains with two, three, or four carbons are as strongly helix stabilizing as the single methyl in alanine and that all linear side chains are stronger helix promoters than leucine. In addition, a t-butyl side chain is significantly more helix destabilizing than the sec-butyl side chain of isoleucine, the isopropyl side chain of valine, or even the unrestricted side chain of glycine. These results provide experimental evidence that restriction in conformational freedom of a side chain imposed by α-helix formation is a major component of the role of a side chain in stabilizing helical structure.

Original languageEnglish (US)
Pages (from-to)5317-5320
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Volume88
Issue number12
DOIs
StatePublished - 1991

Keywords

  • protein folding
  • side chain conformation
  • unnatural amino acids
  • α-helix
  • β-branching

ASJC Scopus subject areas

  • General

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