A. Chakrabartty et al., HELIX CAPPING PROPENSITIES IN PEPTIDES PARALLEL THOSE IN PROTEINS, Proceedings of the National Academy of Sciences of the United Statesof America, 90(23), 1993, pp. 11332-11336
Helix content of peptides with various uncharged nonaromatic amino aci
ds 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 stab
ility: asparagine is the best, glycine is very good, and glutamine is
the worst helix-stabilizing amino acid at this position. The rank orde
r of helix stabilization parallels the frequencies of these amino acid
s at the N-terminal boundary (N-cap) position of helices in proteins f
ound 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 e
ffect on helix stability. N-capping interactions may be responsible fo
r the asymmetric distribution of helix content within a given peptide
found by various workers. An acetyl group on the N-terminal alpha-amin
o function cancels the N-cap effect and the acetyl group is equivalent
to N-terminal asparagine in an unacetylated peptide. Our results demo
nstrate a close relationship between the mechanisms of alpha-helix for
mation in peptides and in proteins.