4fer | pdb_00004fer
Crystal structure of Bacillus Subtilis expansin (EXLX1) in complex with cellohexaose
Structural highlights
Function[YOAJ_BACSU] May promote colonization of plant roots. May cause loosening and extension of plant cell walls by disrupting non-covalent bonding between cellulose microfibrils and matrix glucans. Has very low expansin activity (in vitro). No enzymatic activity has been found. Binds to peptidoglycan and to plant cell walls.[1] Publication Abstract from PubMedComponents of modular cellulases, type-A cellulose-binding modules (CBMs) bind to crystalline cellulose and enhance enzyme effectiveness, but structural details of the interaction are uncertain. We analyzed cellulose binding by EXLX1, a bacterial expansin with ability to loosen plant cell walls and whose domain D2 has type-A CBM characteristics. EXLX1 strongly binds to crystalline cellulose via D2, whereas its affinity for soluble cellooligosaccharides is weak. Calorimetry indicated cellulose binding was largely entropically driven. We solved the crystal structures of EXLX1 complexed with cellulose-like oligosaccharides to find that EXLX1 binds the ligands through hydrophobic interactions of three linearly arranged aromatic residues in D2. The crystal structures revealed a unique form of ligand-mediated dimerization, with the oligosaccharide sandwiched between two D2 domains in opposite polarity. This report clarifies the molecular target of expansin and the specific molecular interactions of a type-A CBM with cellulose. Structural basis for entropy-driven cellulose binding by a type-A cellulose-binding module (CBM) and bacterial expansin.,Georgelis N, Yennawar NH, Cosgrove DJ Proc Natl Acad Sci U S A. 2012 Sep 11;109(37):14830-5. Epub 2012 Aug 27. PMID:22927418[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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