J Biol Chem. 2015 Oct 21. pii: jbc.M115.688630. [Epub ahead of print]
An important facet of the interaction between the pathogen Streptococcus pneumoniae (pneumococcus) and its human host is the ability of this bacterium to process host glycans. To achieve cleavage of the glycosidic bonds in host glycans, S. pneumoniae deploys a wide array of glycoside hydrolases. Here we identify and characterize a new family 20 glycoside hydrolase, GH20C, from S. pneumoniae. Recombinant GH20C possessed the ability to hydrolyze the β-linkages joining either N-acetylglucosamine or N-acetylgalactosamine to a wide variety of aglycon residues, thus revealing this enzyme to be a generalist N-acetylhexosaminidase in vitro. X-ray crystal structures were determined for GH20C in apo-form, in complex with the N-acetylglucosamine and N-acetylgalactosamine products of catalysis, and in complex with both gluco- and galacto-configured inhibitors (PUGNAc, GalPUGNAc, NGT, and GalNGT) at resolutions from 1.84 Å to 2.7 Å. These structures showed N-acetylglucosamine and N-acetylgalactosamine to be recognized via identical sets of molecular interactions. Though the same sets of interaction were maintained with the gluco- and galacto-configured inhibitors, the inhibition constants suggested preferred recognition of the axial O4 when an aglycon moiety was present (Ki for PUGNAc > GalPUGNAc) but preferred recognition of an equatorial O4 when the aglycon was absent (Ki for GalNGT > NGT). Overall, this study reveals GH20C to be another tool that is unique in the arsenal of S. pneumoniae and that it may implement in the effort of the bacterium to utilize and/or destroy the wide array of host glycans that it may encounter.
Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
Streptococcus; X-ray crystallography; enzyme inhibitor; glycobiology; glycoside hydrolase
PMID: 26491009 [PubMed - as supplied by publisher]