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Occurrence and role ofcis peptide bonds in protein structures

1990; Elsevier BV; Volume: 214; Issue: 1 Linguagem: Inglês

10.1016/0022-2836(90)90159-j

1089-8638

David E. Stewart, Atom Sarkar, John E. Wampler,

Chemical Synthesis and Analysis

It has been widely assumed that the occurrence ofcis peptide bonds in proteins is quite rare due to unfavorable contacts between adjacent amino acid residues in this isomeric form. To investigate this assumption, the Brookhaven Protein Data Bank was examined for the occurrences ofcis peptide bonds. Out of 31,005 amide bonds, only 17, or 0.05%, arecis, while 99 of the 1534 imide bonds (X-Pro), or 6.5%, arecis. These figures are considerably less than the distribution predicted on the basis of the potential energy difference between thecis andtrans isomeric forms and experimental data on small peptides. It is not known whether the lower than expected occurrence ofcis peptide bonds arises from constraints imposed by the protein environment, or from assumptions made in the solution of the X-ray crystal structures. However, when the occurrence ofcis bonds in the data base is examined relative to the resolution of the structures, the number ofcis bonds increases with increasing resolution. The distributions seen for these peptide ω bonds in the data base are not the same shape as the distributions predicted from simple potential energy barriers. They are sharper in the main, but they are also broader at the base with significant numbers of non-planar peptide bonds.Cis peptide bonds are found primarily in bends and turns and, in the case ofcis imide bonds (X-PRO), this correlation is so high that it suggests a specific role forcis imide groups in such structures.