Helix stop signals in proteins and peptides: the capping box.
The alpha-helix [Pauling, L., Corey, R. B., & Branson, H. R. (1951) Proc. Natl. Acad. Sci. U.S.A. 37, 205-211] is a common motif in both proteins and peptides. Despite intense investigation, predictive understanding of helices is still lacking. A recent hypothesis [Presta, L. G., & Rose, G. D. (1988) Science 240, 1632-1641] proposed that the structural specificity of helices resides, in part, in those residues that flank helix termini. If so, then signals that arrest helix propagation--i.e., helix stop signals--should be found among these flanking residues. Evidence is presented for the existence of one such signal, a reciprocal backbone-side-chain hydrogen-bonding interaction, dubbed the capping box. In proteins, the capping box is found uniquely at helix N-termini. In peptides, the capping box can function as a helix stop signal, as shown in the work of Kallenbach and co-workers.
Harper
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Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110.
Rose
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GD
D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*
D010455:Peptides; D011506:Proteins