Cloning of cDNA sequences encoding cowpea (Vigna unguiculata) vicilins:
Computational simulations suggest a binding mode of cowpea vicilins to
chitin oligomers
INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES, (2018)DOI: 10.1016/j.ijbiomac.2018.05.197
Abstract
Vicilins are 7S globulins which constitute the major seed storage
proteins in leguminous species. Variant vicilins showing differential
binding affinities for chitin have been implicated in the resistance and
susceptibility of cow pea to the bruchid Callosobruchus maculatus. These
proteins are members of the cupin superfamily, which includes a wide
variety of enzymes and non-catalytic seed storage proteins. The cupin
fold does not share similarity with any known chitin-biding domain.
Therefore, it is poorly understood how these storage proteins bind to
chitin. In this work, partial cDNA sequences encoding beta-vignin, the
major component of cowpea vicilins, were obtained from developing seeds.
Three-dimensional molecular models of beta-vignin showed the
characteristic cupin fold and computational simulations revealed that
each vicilin trimer contained 3 chitin-binding sites. Interaction models
showed that chito-oligosaccharides bound to beta-vignin were stabilized
mainly by hydrogen bonds, a common structural feature of typical
carbohydrate-binding proteins. Furthermore, many of the residues
involved in the chitin-binding sites of beta-vignin are conserved in
other 7S globulins. These results support previous experimental
evidences on the ability of vicilin-like proteins from cowpea and other
leguminous species to bind in vitro to chitin as well as in vivo to
chitinous structures of larval C maculates midgut. (C) 2018 Elsevier
B.V. All rights reserved.