title: Three-dimensional structure of (1,4)-beta-D-mannan mannanohydrolase from tomato fruit.
abstract: The three-dimensional crystal structure of tomato (Lycopersicon esculentum) beta-mannanase 4a (LeMAN4a) has been determined to 1.5 A resolution. The enzyme adopts the (beta/alpha)(8) fold common to the members of glycohydrolase family GH5. The structure is comparable with those of the homologous Trichoderma reesei and Thermomonospora fusca beta-mannanases: There is a conserved three-stranded beta-sheet located near the N terminus that stacks against the central beta-barrel at the end opposite the active site. Three noncanonical beta-helices surround the active site. Similar helices are found in T. reesei but not T. fusca beta-mannanase. By analogy with other beta-mannanases, the catalytic acid/base residue is E204 and the nucleophile residue is E318. The active site cleft of L. esculentum beta-mannanase most closely resembles that of the T. reesei isozyme. A model of substrate binding in LeMAN4a is proposed in which the mannosyl residue occupying the -1 subsite of the enzyme adopts the (1)S(5) skew-boat conformation.
authors.affiliation: Department of Botany, University of Guelph, Ontario, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Bourgault
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Oakley
authors.forename: J Derek
authors.initials: JD
authors.lastname: Bewley
authors.forename: Matthew C J
authors.initials: MC
authors.lastname: Wilce
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D006867:Hydrolases / Q000737:chemistry*; D018551:Solanum lycopersicum / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D010940:Plant Proteins; D006867:Hydrolases