2hcz
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(New page: 200px<br /><applet load="2hcz" size="450" color="white" frame="true" align="right" spinBox="true" caption="2hcz, resolution 2.750Å" /> '''Crystal structure o...)
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Revision as of 09:33, 21 November 2007
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Crystal structure of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize
Overview
Expansins are small extracellular proteins that promote turgor-driven, extension of plant cell walls. EXPB1 (also called Zea m 1) is a member of, the beta-expansin subfamily known in the allergen literature as group-1, grass pollen allergens. EXPB1 induces extension and stress relaxation of, grass cell walls. To help elucidate expansin's mechanism of wall, loosening, we determined the structure of EXPB1 by x-ray crystallography, to 2.75-A resolution. EXPB1 consists of two domains closely packed and, aligned so as to form a long, shallow groove with potential to bind a, glycan backbone of approximately 10 sugar residues. The structure of EXPB1, domain 1 resembles that of family-45 glycoside hydrolase (GH45), with, conservation of most of the residues in the catalytic site. However, EXPB1, lacks a second aspartate that serves as the catalytic base required for, hydrolytic activity in GH45 enzymes. Domain 2 of EXPB1 is an Ig-like, beta-sandwich, with aromatic and polar residues that form a potential, surface for polysaccharide binding in line with the glycan binding cleft, of domain 1. EXPB1 binds to maize cell walls, most strongly to xylans, causing swelling of the cell wall. Tests for hydrolytic activity by EXPB1, with various wall polysaccharides proved negative. Moreover, GH45 enzymes, and a GH45-related protein called "swollenin" lacked wall extension, activity comparable to that of expansins. We propose a model of expansin, action in which EXPB1 facilitates the local movement and stress relaxation, of arabinoxylan-cellulose networks within the wall by noncovalent, rearrangement of its target.
About this Structure
2HCZ is a Single protein structure of sequence from Zea mays with MAN and FCA as ligands. Full crystallographic information is available from OCA.
Reference
Crystal structure and activities of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize., Yennawar NH, Li LC, Dudzinski DM, Tabuchi A, Cosgrove DJ, Proc Natl Acad Sci U S A. 2006 Oct 3;103(40):14664-71. Epub 2006 Sep 19. PMID:16984999
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