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Divalent metal activation of a GH43 β-xylosidase

Paper ID Volume ID Publish Year Pages File Format Full-Text
17079 42639 2013 7 PDF Available
Title
Divalent metal activation of a GH43 β-xylosidase
Abstract

Depolymerization of xylan, a major fraction of lignocellulosic biomass, releases xylose which can be converted into transportation fuels and chemical feedstocks. A requisite enzyme for the breakdown of xylan is β-xylosidase. A gene encoding the 324-amino acid β-xylosidase, RS223-BX, was cloned from an anaerobic mixed microbial culture. This glycoside hydrolase belongs to family 43. Unlike other GH43 enzymes, RS223-BX can be strongly activated by exogenously supplied Ca2+, Co2+, Fe2+, Mg2+, Mn2+ and Ni2+ (e.g., 28-fold by Mg2+) and it is inhibited by Cu2+ or Zn2+. Sedimentation equilibrium centrifugation experiments indicated that the divalent metal cations mediate multimerization of the enzyme from a dimeric to a tetrameric state, which have equal catalytic activity on an active-site basis. Compared to the determined active sites of other GH43 β-xylosidases, the predicted active site of RS223-BX contains two additional amino acids with carboxylated side chains that provide potential sites for divalent metal cations to reside. Thus, the divalent metal cations likely occupy the active site and participate in the catalytic mechanism. RS223-BX accepts as substrate xylobiose, arabinobiose, 4-nitrophenyl-β-d-xylopyranoside, and 4-nitrophenyl-α-l-arabinofuranoside. Additionally, the enzyme has good pH and temperature stabilities and a large Ki for d-glucose (1.3 M), favorable properties for performance in saccharification reactors.

► A GH43 β-xylosidase was isolated from a waste water treatment facility. ► The enzyme was characterized by activity assays and analytical centrifugation. ► The β-xylosidase has high activity acting on native substrate xylobiose. ► This is the first GH43 enzyme reported to be highly activated by divalent cations. ► Divalent metal cations mediate tetramerization of the β-xylosidase.

Keywords
β-Xylosidase; Divalent cation; Hemicellulose; Multimerization
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Publisher
Database: Elsevier - ScienceDirect
Journal: Enzyme and Microbial Technology - Volume 52, Issue 2, 5 February 2013, Pages 84–90
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us