title: Helix capping propensities in peptides parallel those in proteins.
abstract: Helix content of peptides with various uncharged nonaromatic amino acids at either the N-terminal or C-terminal position has been determined. The choice of N-terminal amino acid has a major effect on helix stability: asparagine is the best, glycine is very good, and glutamine is the worst helix-stabilizing amino acid at this position. The rank order of helix stabilization parallels the frequencies of these amino acids at the N-terminal boundary (N-cap) position of helices in proteins found by Richardson and Richardson [Richardson, J. S. & Richardson, D. C. (1988) Science 240, 1648-1652], and the N-terminal amino acid in a peptide composed of helix-forming amino acids may be considered as the N-cap residue. The choice of C-terminal amino acid has only a minor effect on helix stability. N-capping interactions may be responsible for the asymmetric distribution of helix content within a given peptide found by various workers. An acetyl group on the N-terminal alpha-amino function cancels the N-cap effect and the acetyl group is equivalent to N-terminal asparagine in an unacetylated peptide. Our results demonstrate a close relationship between the mechanisms of alpha-helix formation in peptides and in proteins.
authors.affiliation: Department of Biochemistry, Beckman Center, Stanford University Medical School, CA 94305-5307.
authors.forename: A
authors.initials: A
authors.lastname: Chakrabartty
authors.forename: A J
authors.initials: AJ
authors.lastname: Doig
authors.forename: R L
authors.initials: RL
authors.lastname: Baldwin
mesh_terms: D000107:Acetylation; D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D010455:Peptides; D000409:Alanine