1cnv
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(New page: 200px<br /><applet load="1cnv" size="450" color="white" frame="true" align="right" spinBox="true" caption="1cnv, resolution 1.65Å" /> '''CRYSTAL STRUCTURE OF...)
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Revision as of 10:29, 20 November 2007
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CRYSTAL STRUCTURE OF CONCANAVALIN B AT 1.65 A RESOLUTION
Overview
Seeds of Canavalia ensiformis (jack bean) contain besides large amounts of, canavalin and concanavalin A, a protein with a molecular mass of 33,800, which has been named concanavalin B. Although concanavalin B shares about, 40% sequence identity with plant chitinases belonging to glycosyl, hydrolase family 18, no chitinase activity could be detected for this, protein. To resolve this incongruity concanavalin B was crystallised and, its three-dimensional structure determined at 1.65 A (1 A = 0.1 nm), resolution. The structure consists of a single domain with a (beta/alpha)8, topology. A 30 amino acid residue long loop occurs between the second, beta-strand of the barrel and the second alpha-helix. This extended loop, is unusual for the (beta/alpha)8 topology, but appears in a similar, conformation in the structures of the seed protein narbonin and several, chitinases as well. Two non-proline cis-peptide bonds are present in the, structure of concanavalin B: Ser34-Phe, and Trp265-Asn. This structural, feature is rarely observed in proteins, but could also be identified in, the three-dimensional structures of family 18 chitinases and narbonin in, coincident positions. In the chitinases the aromatic residues of the, non-proline cis-peptides have been proposed to have a function in the, binding of the substrate. The region in concanavalin B, where in, chitinases the active site is located, shows two significant differences., First, the catalytic glutamic acid is a glutamine in concanavalin B., Second, although part of the substrate binding cleft of the chitinases is, present in concanavalin B, it is much shorter. From this we conclude that, concanavalin B and family 18 chitinases are closely related, but that, concanavalin B has lost its enzymatic function. It still may act as a, carbohydrate binding protein, however.
About this Structure
1CNV is a Single protein structure of sequence from Canavalia ensiformis. Full crystallographic information is available from OCA.
Reference
Crystal structure of concanavalin B at 1.65 A resolution. An "inactivated" chitinase from seeds of Canavalia ensiformis., Hennig M, Jansonius JN, Terwisscha van Scheltinga AC, Dijkstra BW, Schlesier B, J Mol Biol. 1995 Nov 24;254(2):237-46. PMID:7490746
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