Calculated probabilities of bend formation in 47 amino acid sequences of
N-acetyl-N'-methylamide dipeptides, determined from a statistical mechanical analysis using empirical conformational energies, were compared with the observed fraction of
bends formed in the same 47
dipeptide sequences in the x-ray structures of 20 globular
proteins. Agreement between the calculated and observed fraction of
bends was found for 26
dipeptides, suggesting that, for those particular
dipeptide sequences, local interactions dominate over long-range interactions in determining conformational preference. Seven
dipeptide sequences, all of which contained a Gly residue, had a significantly higher calculated than observed bend preference, indicating the strong influence of long-range and/or
solvent interactions in those sequences. Of the 14 sequences for which the calculated was significantly less than the observed bend fraction, 13
dipeptide sequences contained at least one polar residue (Ser, Asn, or Asp) and/or an aromatic residue (Phe or Tyr), suggesting that
solvent effects may play an important role in dictating the conformation in these sequences. The analysis of
dipeptide sequences in the twenty globular
proteins also indicated that the 4 leads to 1 hydrogen bond is not a dominant factor in stabilizing
bends in
proteins, and that most
dipeptide sequences are capable of forming several types of bend conformations.