Crystal structure and identification of amino acid residues for catalysis and binding of GH3 AnBX β-xylosidase from Aspergillus niger

Wilaiwan Kaenying, Khuanjarat Choengpanya, Takayoshi Tagami, Pakorn Wattana-Amorn, Weeranuch Lang, Masayuki Okuyama, Yaw Kuen Li, Atsuo Kimura, Prachumporn T. Kongsaeree*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Abstract: β-Xylosidases catalyze the hydrolysis of xylooligosaccharides to xylose in the final step of hemicellulose degradation. AnBX, which is a GH3 β-xylosidase from Aspergillus niger, has a high catalytic efficiency toward xyloside substrates. In this study, we report the three-dimensional structure and the identification of catalytic and substrate binding residues of AnBX by performing site-directed mutagenesis, kinetic analysis, and NMR spectroscopy-associated analysis of the azide rescue reaction. The structure of the E88A mutant of AnBX, determined at 2.5-Å resolution, contains two molecules in the asymmetric unit, each of which is composed of three domains, namely an N-terminal (β/α)8 TIM-barrel-like domain, an (α/β)6 sandwich domain, and a C-terminal fibronectin type III domain. Asp288 and Glu500 of AnBX were experimentally confirmed to act as the catalytic nucleophile and acid/base catalyst, respectively. The crystal structure revealed that Trp86, Glu88 and Cys289, which formed a disulfide bond with Cys321, were located at subsite -1. Although the E88D and C289W mutations reduced catalytic efficiency toward all four substrates tested, the substitution of Trp86 with Ala, Asp and Ser increased the substrate preference for glucoside relative to xyloside substrates, indicating that Trp86 is responsible for the xyloside specificity of AnBX. The structural and biochemical information of AnBX obtained in this study provides invaluable insight into modulating the enzymatic properties for the hydrolysis of lignocellulosic biomass.

Original languageEnglish
Pages (from-to)2335-2349
Number of pages15
JournalApplied Microbiology and Biotechnology
Volume107
Issue number7-8
DOIs
StatePublished - Apr 2023

Keywords

  • Acid/Base catalyst
  • Crystal structure
  • Glycone specificity
  • Glycoside hydrolase family 3
  • β-Xylosidase

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