Straight-chain non-polar amino acids are good helix-formers in water.
For comparison with earlier data on naturally occurring non-polar amino acids (Ala, Leu, Phe, Val, Ile), the comparative helix-forming tendencies have been measured for non-polar amino acid residues that have unbranched side-chains, with an ethyl, propyl or butyl group, and also for methionine. The substitutions are made in a 17-residue alanine-based peptide. The results show that straight-chain non-polar amino acids have high helix-forming tendencies compared to beta-branched non-polar amino acids. Restriction of side-chain conformations in the helix, with a corresponding reduction in conformational entropy, is the likely explanation. There is a small increase in helix-forming tendency as the side-chain increases in length from ethyl to butyl, which suggests that a helix-stabilizing hydrophobic interaction is being detected.
Padmanabhan
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Department of Biochemistry, Stanford University Medical School, CA 94305.
Baldwin
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RL
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D007532:Isoleucine / Q000737:chemistry; D007930:Leucine / Q000737:chemistry; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D014633:Valine / Q000737:chemistry; D014867:Water
D000596:Amino Acids; D010455:Peptides; D007532:Isoleucine; D014867:Water; D010649:Phenylalanine; D007930:Leucine; D014633:Valine; D000409:Alanine