Ramachandran, GN and Mitra, Alok K (1976) An explanation for the rare occurrence of cis peptide units in proteins and polypeptides. In: Journal of Molecular Biology, 107 (1). pp. 85-92.
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The rarity of occurrence of cis peptide units is only partially explained by the higher intrinsic energy of the cis over the trans form, which provides a probability of 0·01 for cis peptide units to occur. An additional factor is the conformational restriction imposed by the occurrence of a cis peptide unit in a chain of trans units. Taking a section of three peptide units having the sequences trans-trans-trans (ttt) and trans-cis-trans (tct), conformational energy calculations indicate that the latter can occur only to an extent of 0·1%, unless there occurs the sequence X-Pro, in which case it is of the order of 30%. This explains the extreme rarity of cis peptide units, in general; however, it follows that even with non-prolyl residues, cis peptide units are not forbidden, but can occur in some rare examples and should be looked for.
|Item Type:||Journal Article|
|Additional Information:||Copyright of this article belongs to Elsevier Science.|
|Department/Centre:||Division of Biological Sciences > Molecular Biophysics Unit|
|Date Deposited:||11 Dec 2009 06:56|
|Last Modified:||19 Sep 2010 05:48|
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