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J Biol Chem. 2018 Sep 24. pii: jbc.RA118.003302. doi: 10.1074/jbc.RA118.003302. [Epub ahead of print]

Functional metagenomics identifies an exosialidase with an inverting catalytic mechanism that defines a new glycoside hydrolase family (GH156).

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New England Biolabs, United States.
Max Planck Institute for Dynamics of Complex Technical Systems, Bioprocess Engineering, Germany.
CNRS & Universities of Aix-Marseille, France.
Protein Expression & Modification Division, New England Biolabs, United States.


Exosialidases are glycoside hydrolases that remove a single terminal sialic acid residue from oligosaccharides. They are widely distributed in biology, having been found in prokaryotes, eukaryotes, and certain viruses. Most characterized prokaryotic sialidases are from organisms that are pathogenic or commensal with mammals. However, in this study, we used functional metagenomic screening to seek microbial sialidases encoded by environmental DNA isolated from an extreme ecological niche, a thermal spring. Using recombinant expression of potential exosialidase candidates and a fluorogenic sialidase substrate, we discovered an exosialidase having no homology to known sialidases. Phylogenetic analysis indicated that this protein is a member of a small family of bacterial proteins of previously unknown function. Proton NMR revealed that this enzyme functions via an inverting catalytic mechanism, a biochemical property that is distinct from those of known exosialidases. This unique inverting exosialidase defines a new CAZy glycoside hydrolase family we have designated GH156.


extremophile; functional metagenomics; glycoside hydrolase; glycosylation; high-throughput screening (HTS); inverting mechanism; neuraminidase; sialic acid; sialidase

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