Structure of a glycoside hydrolase family 50 enzyme from a subfamily that is enriched in human gut microbiome bacteroidetes

The polysaccharide utilization locus in Bacteroides plebeius that confers the ability to catabolize porphyran contains a putative GH50 β‐agarase (BACPLE_01683, BpGH50). BpGH50 did not show any clear activity on agarose or on the related algal galactans porphyran and carrageenan. However, the 1.4 Å resolution X‐ray crystal structure of BpGH50 confirmed its possession of the core (α/β)₈ barrel fold found in GH50 enzymes as well as the structural conservation of the catalytic residues and some substrate binding residues. Examination of the structure supports assignment of this protein as a β‐galactosidase but suggests that it may utilize a different, possibly hybrid, algal galactan substrate. Proteins 2016; 85:182–187. © 2016 Wiley Periodicals, Inc.