Highly restricted distributions of hydrophobic and charged amino acids in longitudinal quadrants of α-helices

R. R. Torgerson, R. A. Lew, V. E. Reyes, L. Hardy, R. E. Humphreys

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15 Scopus citations


Helix formation in folding proteins is stabilized by binding of recurrent hydrophobic side chains in one longitudinal quadrant against the locally most hydrophobic region of the protein. To test this hypothesis, we fitted sequences of 247 α-helices of 55 proteins to the circular (infinite) template to maximize the strip-of-helix hydrophobicity index (the mean hydrophobicity of residues in positions). These template-predicted configurations closely matched crystallograhic structures in 87% of four- or five-turn helices compared. We determined the longitudinal quadrant distributions of amino acids in the template-fitted, sheet projections of α-helices with respect to the best longitudinal, hydrophobic strip on each helix and to the N and C termini, interiors, and entire helices. Amino acids Leu, Ile, Val, and Phe were concentrated in one longitudinal quadrant (p < 0.001). Lys, Arg, Asp, and Glu were not in the quadrant of Leu, Ile, Val, and Phe (p < 0.001). Significant quadrant distributions for other amino acids and for termini of the helices were also found.

Original languageEnglish (US)
Pages (from-to)5521-5524
Number of pages4
JournalJournal of Biological Chemistry
Issue number9
StatePublished - Oct 22 1991
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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