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Alpha-Turns In Protein Structures

Natraj, DV and Srinivasan, N and Sowdhamini, R and Ramakrishnan, C (1995) Alpha-Turns In Protein Structures. In: Current Science, 69 (5). pp. 434-447.

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Abstract

The occurrence of 5 --> 1 type of hydrogen bonds (alpha-turn) in proteins has been studied using a data set comprising of 107 proteins with resolution less than or equal to 2.0 Angstrom. A very large majority of such alpha-turn segments (96%) form part of regular alpha-helices. The examples (84) which do not form part of an alpha-helix are termed 'isolated alpha-turns' and are grouped into two major families and seven minor groups along with two isolated examples based on the similarity of conformational angles, The family with large number of examples (50) have (phi, psi) angles close to an alpha-helix and hence belong to the class of the shortest alpha-helices, The 'end to end' distances of these alpha-turns vary between 4.7 and 6.7 Angstrom, the range being nearly the same as that of alpha-helices. The propensity calculations show that some amino acids such as Glu, Ser and Thr have statistically significant higher preferences to occur in alpha-turns than in alpha-helices, In addition to the 5 --> 1 type, the residues in the alpha-turn are involved in hydrogen bonds with other parts of the chain, The residues are in general more hydrophilic compared to those in alpha-helices, In many cases (70%) the alpha-turn occurs at the ends of extended strands, and whenever it occurs at the loop regions connecting two extended strands, it brings about a hairpin bend.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Current Science Association
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 20 Feb 2009 06:28
Last Modified: 19 Sep 2010 05:26
URI: http://eprints.iisc.ernet.in/id/eprint/19118

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