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X-ray Crystal Structure of Divalent Metal-Activated β-xylosidase, RS223BX
- Douglas B. Jordan, Jay D. Braker, Kurt Wagschal, Charles C. Lee, Victor J. Chan, Ievgeniia Dubrovska, Spencer Anderson, Zdzislaw Wawrzak
- Applied biochemistry and biotechnology 2015 v.177 no.3 pp. 637-648
- X-ray diffraction, histidine, active sites, calcium, cations, divalent metals, glycosides, mutation, xylan 1,4-beta-xylosidase
- 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 Ca²⁺ cation is located at the back of the active-site pocket. The Ca²⁺ is held in the active site by the carboxylate of D85, an “extra” acid residue in comparison to other GH43 active sites. The Ca²⁺ 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.