title: X-ray Crystal Structure of Divalent Metal-Activated β-xylosidase, RS223BX.
abstract: We report the X-ray crystal structure of a glycoside hydrolase family 43 β-xylosidase, RS223BX, which is strongly activated by the addition of divalent metal cations. The 2.69 Å structure reveals that the Ca(2+) cation is located at the back of the active-site pocket. The Ca(2+) is held in the active site by the carboxylate of D85, an "extra" acid residue in comparison to other GH43 active sites. The Ca(2+) is in close contact with a histidine imidazole, which in turn is in contact with the catalytic base (D15) thus providing a mechanism for stabilizing the carboxylate anion of the base and achieve metal activation. The active-site pocket is mirrored by an "inactive-site" pocket of unknown function that resides on the opposite side of the monomer.
authors.affiliation: USDA-ARS-National Center for Agricultural Utilization Research, 1815 N. University St, Peoria, IL, 61604, USA. douglas.jordan@ars.usda.gov.
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Jordan
authors.affiliation: USDA-ARS-National Center for Agricultural Utilization Research, 1815 N. University St, Peoria, IL, 61604, USA.
authors.forename: Jay D
authors.initials: JD
authors.lastname: Braker
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Wagschal
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Lee
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Chan
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA.
authors.forename: Ievgeniia
authors.initials: I
authors.lastname: Dubrovska
authors.affiliation: Synchrotron Research Center, Northwestern University, 9700 S Cass Ave, Argonne, IL, 60439, USA.
authors.forename: Spencer
authors.initials: S
authors.lastname: Anderson
authors.affiliation: Synchrotron Research Center, Northwestern University, 9700 S Cass Ave, Argonne, IL, 60439, USA.
authors.forename: Zdzislaw
authors.initials: Z
authors.lastname: Wawrzak
mesh_terms: D020134:Catalytic Domain; D002413:Cations, Divalent / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D004789:Enzyme Activation / Q000187:drug effects; D008958:Models, Molecular; D014995:Xylosidases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase
keywords: Activation; Divalent metal cations; GH43 β-xylosidase; Inverting mechanism