# Occurrence and geometrical features of head-to-tail sequences involving amino acids in crystal structures

Suresh, CG and Vijayan, M (1983) Occurrence and geometrical features of head-to-tail sequences involving amino acids in crystal structures. In: International Journal of Peptide & Protein Research, 22 (2). pp. 129-143.

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## Abstract

A careful study of the crystal structures of commonly occurring amino acids and their racemates and complexes reveals that each H bond connecting the \alpha-amino and the \alpha-carboxylate groups and its symmetry equivalent generally give rise to an infinite head-to-tail sequence in which the 2 groups are periodically brought into close proximity. Such sequences, which have earlier been suggested to be of probable relevance to prebiotic polymeriation, appear to be an almost universal feature of amino acid aggregation in the solid state. These sequences belong to 2 main categories in terms of the geometrical arrangement of amino acid molecules in them. The sequences in the 1st category consist of straight chains of molecules related mostly by the shortest cell translation in the crystals. The sequences of the 2nd category form H-bonded 2-fold helixes centered around crystallography 21 screw axes. The sequences can be further subdivided into different types on the basis of the geometrical features of the H bonds involved in them. A few sequences involving both L and D isomers have also been observed in the crystal structures of some DL-amino acids. The shortest cell translation in most crystals under consideration has a value of $\sim 5.3 \AA$ and corresponds to the periodicity of a straight head-to-tail sequence or, less frequently, that of a helical sequence or both. The crystal structures of amino acids and their complexes can be classified in terms of the occurrence and the geometrical disposition of different types of head-to-tail sequences in them.

Item Type: Journal Article International Journal of Peptide & Protein Research Copenhagen : Munksgaard Copyright of this article belongs to Copenhagen: Munksgaard. Division of Biological Sciences > Molecular Biophysics Unit 22 Jul 2008 27 Aug 2008 13:37 http://eprints.iisc.ac.in/id/eprint/15154