|DUBROVSKA, IEVGENIIA - Northwestern University|
|ANDERSON, SPENCER - Northwestern University|
|WAWRZAK, ZDZISLAW - Northwestern University|
Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2015
Publication Date: 7/23/2015
Publication URL: https://handle.nal.usda.gov/10113/62506
Citation: Jordan, D.B., Braker, J.D., Wagschal, K., Lee, C.C., Chan, V.J., Dubrovska, I., Anderson, S., Wawrzak, Z. 2015. X-ray crystal structure of divalent metal-activated ß-xyloisdase, RS223BX. Applied Biochemistry and Biotechnology. 177:637-648. doi: 10.1007/s12010-015-1767-z.
Interpretive Summary: More efficient enzymes for breaking down cellulose and hemicellulose are needed to bring down production costs of bioethanol and other biofuels. This paper describes the X-ray structure of a ß-xylosidase that has the highest activity for the kcat/Km parameter of any enzyme acting on xylooligosaccharides, the natural substrate. The structure reveals a new role for divalent metal activation of glycoside hydrolases.
Technical Abstract: We report the first X-ray structure of a glycoside hydrolase family 43 ß-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+ coordinates to H274 to stabilize an imidazolium, which in turn stabilizes the catalytic base (D15 carboxyl group) as the anion. This is a new catalytic role for divalent metal cations among glycoside hydrolases. The active-site pocket is mirrored by an “inactive-site” pocket of unknown function that resides on the opposite side of the monomer. Virtual mutation of two residues to alanines creates a tunnel that spans the monomer. The “inactive-site” pocket is found in all 20 of the glycoside hydrolase family 43 X-ray structures.