title: First crystallographic structure of a xylanase from glycoside hydrolase family 5: implications for catalysis.
abstract: The room-temperature structure of xylanase (EC 3.2.1.8) from the bacterial plant pathogen Erwinia chrysanthemi expressed in Escherichia coli, a 45 kDa, 413-amino acid protein belonging to glycoside hydrolase family 5, has been determined by multiple isomorphous replacement and refined to a resolution of 1.42 A. This represents the first structure of a xylanase not belonging to either glycoside hydrolase family 10 or family 11. The enzyme is composed of two domains similar to most family 10 xylanases and the alpha-amylases. The catalytic domain (residues 46-315) has a (beta/alpha)(8)-barrel motif with a binding cleft along the C-terminal side of the beta-barrel. The catalytic residues, Glu165 and Glu253, determined by correspondence to other family 5 and family 10 glycoside hydrolases, lie inside this cleft on the C-terminal ends of beta-strands 4 and 7, respectively, with an O(epsilon)2...O(epsilon)1 distance of 4.22 A. The smaller domain (residues 31-43 and 323-413) has a beta(9)-barrel motif with five of the strands interfacing with alpha-helices 7 and 8 of the catalytic domain. The first 13 N-terminal residues form one beta-strand of this domain. Residues 44, 45, and 316-322 form the linkers between this domain and the catalytic domain.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, USA.
authors.forename: Steven B
authors.initials: SB
authors.lastname: Larson
authors.forename: John
authors.initials: J
authors.lastname: Day
authors.forename: Ana Paulina
authors.initials: AP
authors.lastname: Barba de la  Rosa
authors.forename: Noel T
authors.initials: NT
authors.lastname: Keen
authors.forename: Alexander
authors.initials: A
authors.lastname: McPherson
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray / Q000379:methods; D016974:Dickeya chrysanthemi / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D006026:Glycoside Hydrolases / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D043325:Xylan Endo-1,3-beta-Xylosidase; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D006026:Glycoside Hydrolases; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase