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

J Biol Chem. 2018 Nov 23;293(47):18138-18150. doi: 10.1074/jbc.RA118.003302. Epub 2018 Sep 24.


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.

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

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacteria / classification
  • Bacteria / enzymology*
  • Bacteria / genetics
  • Bacteria / isolation & purification
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Catalytic Domain
  • Enzyme Stability
  • Fresh Water / microbiology
  • Glycoside Hydrolases / chemistry
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / metabolism
  • Hot Temperature
  • Metagenomics
  • Molecular Sequence Data
  • Multigene Family*
  • Neuraminidase / chemistry*
  • Neuraminidase / genetics*
  • Neuraminidase / metabolism
  • Open Reading Frames
  • Phylogeny
  • Substrate Specificity


  • Bacterial Proteins
  • Glycoside Hydrolases
  • Neuraminidase