title: The importance of the Abn2 calcium cluster in the endo-1,5-arabinanase activity from Bacillus subtilis.
abstract: Arabinanase is a glycosyl hydrolase that is able to cleave the glycosidic bonds of α-1,5-L-arabinan, releasing arabino-oligosaccharides and L-arabinose. The enzyme has two domains, an N-terminal catalytic domain with a characteristic β-propeller fold and a C-terminal domain whose function is unknown. A calcium ion, located near the catalytic site, serves to stabilize the N-terminal domain, but it has also been proposed to play a key role in the enzyme mechanism. The present work describes the structure of an inactive mutant of the wild-type enzyme (H318Q) and in which the calcium ion has been adventitiously replaced by nickel. These structural studies, together with functional and modelling studies, clearly support the role of the calcium ion in the overall reaction mechanism.
authors.affiliation: Macromolecular Crystallography Unit, Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, EAN, 2780-157, Oeiras, Protugal.
authors.forename: C E
authors.initials: CE
authors.lastname: McVey
authors.forename: M J
authors.initials: MJ
authors.lastname: Ferreira
authors.forename: B
authors.initials: B
authors.lastname: Correia
authors.forename: S
authors.initials: S
authors.lastname: Lahiri
authors.forename: D
authors.initials: D
authors.lastname: de Sanctis
authors.forename: Maria Arménia
authors.initials: MA
authors.lastname: Carrondo
authors.forename: P F
authors.initials: PF
authors.lastname: Lindley
authors.forename: Isabel
authors.initials: I
authors.lastname: de Sá Nogueira
authors.forename: Cláudio Manuel
authors.initials: CM
authors.lastname: Soares
authors.forename: Isabel
authors.initials: I
authors.lastname: Bento
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology* / Q000378:metabolism*; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism*; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D013379:Substrate Specificity
chemical_list: D006026:Glycoside Hydrolases; D002118:Calcium