Structural analysis of peptide helices containing centrally positioned lactic acid residues |
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Authors: | Aravinda S Shamala N Das Chittaranjan Balaram P |
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Institution: | Department of Physics, Indian Institute of Science, Bangalore- 560 012, India. |
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Abstract: | The effect of insertion of lactic acid (Lac) residues into peptide helices has been probed using specifically designed sequences. The crystal structures of 11-residue and 14-residue depsipeptides Boc-Val-Val-Ala-Leu-Val-Lac-Leu-Aib-Val-Ala-Leu-OMe (1) and Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Val-Lac-Leu-Aib-Val-Ala-Leu-OMe (3), containing centrally positioned Lac residues, have been determined. The structure of an 11-residue peptide Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe (2), analog of a which is an amide previously determined Lac-containing depsipeptide, Boc-Val-Ala-Leu-Aib-Val-Lac-Leu-Aib-Val-Ala-Leu-OMe I. L. Karle, C. Das, and P. Balaram, Biopolymers, Vol. 59, (2001) pp. 276-289], is also reported. Peptide 1 adopts a helical fold, which is stabilized by mixture of 4-->1 and 5-->1 hydrogen bonds. Peptide 2 adopts a completely alpha-helical conformation stabilized by eight successive 5-->1 hydrogen bonds. Peptide 3 appears to be predominately alpha-helical, with seven 5-->1 hydrogen bonds and three 4-->1 interaction interspersed in the sequence. In the structure of peptide 3 in addition to water molecules in the head-to-tail region, hydration at an internal segment of the helix is also observed. A comparison of five related peptide helices, containing a single Lac residue, reveals that the hydroxy acid can be comfortably accommodated at interior positions in the helix, with the closest C=O...O distances lying between 2.8 and 3.3 A. |
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Keywords: | 4→1/5→1 hydrogen bonds depsipeptides α‐helix lactic acid x‐ray crystal structures |
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