# Parallel packing of \alpha-helices in crystals of the zervamicin IIA analog Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe ${2H}_2O$

Karle, Isabella L and Sukumar, Muppalla and Balaram, Padmanabhan (1986) Parallel packing of \alpha-helices in crystals of the zervamicin IIA analog Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe ${2H}_2O$. In: Proceedings of the National Academy of Sciences of the United States of America, 83 (24). pp. 9284-9288.

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## Abstract

An apolar synthetic analog of the first 10 residues at the ${NH}_2$-terminal end of zervamicin IIA crystallizes in the triclinic space group P1 with cell dimensions a = 10.206 \pm 0.002 A, b = 12.244 \pm 0.002 A, c = 15.049 \pm 0.002 A, \alpha = 93.94 \pm 0.010, \beta = 95.10 \pm 0.010, \gamma = 104.56 \pm 0.01 deg, Z = 1, $C_{60}H_{97}N_{11}O_{13}.{2H}_2O$. Despite the relatively few \alpha-aminoisobutyric acid residues, the peptide maintains a helical form. The first intrahelical hydrogen bond is of the $3_{10}$ type between N(3) and O(0), followed by five \alpha-helix-type hydrogen bonds. Solution 1H NMR studies in chloroform also favor a helical conformation, with seven solvent-shielded NH groups. Continuous columns are formed by head-to-tail hydrogen bonds between the helical molecules along the helix axis. The absence of polar side chains precludes any lateral hydrogen bonds. Since the peptide crystallizes with one molecule in a trilinic space group, aggregation of the helical columns must necessarily be parallel rather than antiparallel. The packing of the columns is rather inefficient, as indicated by very few good van der Waals' contacts and the occurrence of voids between the molecules.

Item Type: Journal Article Copyright for this article belongs to National Academy of Sciences. x-ray structure analysis;hydrogen bond;helix curvature;ionophore;membrane channel Division of Biological Sciences > Molecular Biophysics Unit 28 Feb 2005 19 Sep 2010 04:18 http://eprints.iisc.ernet.in/id/eprint/2854