PUL ID

PUL0326

PubMed

28461332, J Biol Chem. 2017 Jun 23;292(25):10639-10650. doi: 10.1074/jbc.M117.787606. Epub 2017 May 1.

Characterization method

gene deletion mutant and growth assay, enzyme activity assay, thin layer chromatography

Genomic accession number

DS264584.1

Nucelotide position range

82516-94883

Substrate

beta-glucan

Loci

BACOVA_RS10410- BACOVA_00946

Species

Bacteroides ovatus/28116

Degradation or Biosynthesis

degradation

Cluster number

1

Gene name

Gene position

Gene type

Found by CGCFinder?

- 1 - 747 (-) CDS No
- 753 - 1409 (-) CDS No
- 1444 - 1620 (-) CDS No
- 1633 - 3189 (-) CAZyme: GH73 Yes
- 3202 - 5463 (-) other Yes
- 5491 - 7290 (-) other Yes
- 7299 - 7580 (-) other Yes
- 7604 - 8434 (-) STP: STP|Peptidase_M23 Yes
- 8459 - 9124 (-) other Yes
- 9139 - 9822 (-) other Yes
- 9837 - 10526 (-) other Yes
- 10507 - 11004 (-) TC: gnl|TC-DB|F0R7G3|9.B.154.1.2 Yes
- 11001 - 12368 (-) CDS No

PUL ID

PUL0326

PubMed

28461332, J Biol Chem. 2017 Jun 23;292(25):10639-10650. doi: 10.1074/jbc.M117.787606. Epub 2017 May 1.

Title

A Bacteroidetes locus dedicated to fungal 1,6-beta-glucan degradation: Unique substrate conformation drives specificity of the key endo-1,6-beta-glucanase.

Author

Temple MJ, Cuskin F, Basle A, Hickey N, Speciale G, Williams SJ, Gilbert HJ, Lowe EC

Abstract

Glycans are major nutrients available to the human gut microbiota. The Bacteroides are generalist glycan degraders, and this function is mediated largely by polysaccharide utilization loci (PULs). The genomes of several Bacteroides species contain a PUL, PUL1,6-beta-glucan, that was predicted to target mixed linked plant 1,3;1,4-beta-glucans. To test this hypothesis we characterized the proteins encoded by this locus in Bacteroides thetaiotaomicron, a member of the human gut microbiota. We show here that PUL1,6-beta-glucan does not orchestrate the degradation of a plant polysaccharide but targets a fungal cell wall glycan, 1,6-beta-glucan, which is a growth substrate for the bacterium. The locus is up-regulated by 1,6-beta-glucan and encodes two enzymes, a surface endo-1,6-beta-glucanase, BT3312, and a periplasmic beta-glucosidase that targets primarily 1,6-beta-glucans. The non-catalytic proteins encoded by PUL1,6-beta-glucan target 1,6-beta-glucans and comprise a surface glycan-binding protein and a SusD homologue that delivers glycans to the outer membrane transporter. We identified the central role of the endo-1,6-beta-glucanase in 1,6-beta-glucan depolymerization by deleting bt3312, which prevented the growth of B. thetaiotaomicron on 1,6-beta-glucan. The crystal structure of BT3312 in complex with beta-glucosyl-1,6-deoxynojirimycin revealed a TIM barrel catalytic domain that contains a deep substrate-binding cleft tailored to accommodate the hook-like structure adopted by 1,6-beta-glucan. Specificity is driven by the complementarity of the enzyme active site cleft and the conformation of the substrate. We also noted that PUL1,6-beta-glucan is syntenic to many PULs from other Bacteroidetes, suggesting that utilization of yeast and fungal cell wall 1,6-beta-glucans is a widespread adaptation within the human microbiota.