Bacteroides thetaiotaomicron generates diverse α-mannosidase activities through subtle evolution of a distal substrate-binding motif

Andrew J. Thompson*, Richard J. Spears, Yanping Zhu, Michael D.L. Suits, Spencer J. Williams, Harry J. Gilbert, Gideon J. Davies

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


A dominant human gut microbe, the well studied symbiont Bacteroides thetaiotaomicron (Bt), is a glyco-specialist that harbors a large repertoire of genes devoted to carbohydrate processing. Despite strong similarities among them, many of the encoded enzymes have evolved distinct substrate specificities, and through the clustering of cognate genes within operons termed polysaccharide-utilization loci (PULs) enable the fulfilment of complex biological roles. Structural analyses of two glycoside hydrolase family 92 α-mannosidases, BT3130 and BT3965, together with mechanistically relevant complexes at 1.8–2.5 Å resolution reveal conservation of the global enzyme fold and core catalytic apparatus despite different linkage specificities. Structure comparison shows that Bt differentiates the activity of these enzymes through evolution of a highly variable substrate-binding region immediately adjacent to the active site. These observations unveil a genetic/biochemical mechanism through which polysaccharide-processing bacteria can evolve new and specific biochemical activities from otherwise highly similar gene products.

Original languageEnglish
Pages (from-to)394-404
Number of pages11
JournalActa crystallographica. Section D, Structural biology
Issue number5
Publication statusPublished - 1 May 2018

Bibliographical note

2018, The Author(s).


  • Bacteroides thetaiotaomicron
  • carbohydrates
  • glycans
  • glycoside hydrolase family 92
  • substrate specificity
  • α-mannosidase

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