A Cold- and Salt-Tolerant GH43-1 β-Xylosidase from Cellulomonas bogoriensis 69B4^T: Biochemical Characterization and...

The β-xylosidase Cbxyl1 of GH43-1 subfamily from Cellulomonas bogoriensis 69B4^T was expressed in Escherichia coli. It showed optimal activity at 30 °C and pH 7.0, retaining 40% of its activity at 10 °C. It displayed Ca²⁺-dependent activity and remarkable salt tolerance, maintaining 87% activity in the presence of 4 M KCl. Cbxyl1 hydrolyzed p-nitrophenyl-β-D-xylopyranoside, p-nitrophenyl-α-L-arabinofuranoside, and xylooligosaccharides, but could not cleave arabinose from arabinoxylan oligosaccharides. Structural analysis reveals that Cbxyl1 adopts a five-bladed β-propeller fold characteristic of the GH43 family, with Asp5, Asp125, and Glu212 as the catalytic residues, along with a high proportion of random coils and a low number of salt bridges and hydrogen bonds. Phylogenetic analysis and comparison with other GH43-1 enzymes suggest functional diversity within this subfamily, including both strict β-xylosidases and bifunctional enzymes. Collectively, these results establish Cbxyl1 as a cold- and salt-tolerant β-xylosidase with strict substrate selectivity, thereby providing a candidate enzyme together with experimental information for further investigation and potential application, and contributing to a refined understanding of the substrate specificity landscape within the GH43-1 subfamily.