Glycosyl transferase GT2 genes mediate the biosynthesis of an unusual (1,3;1,4)-β-glucan exopolysaccharide in the bacterium Sarcina ventriculi

Edwin R. Lampugnani, Kris Ford, Yin Ying Ho, Allison van de Meene, Jelle Lahnstein, Hwei Ting Tan, Rachel A. Burton, Geoffrey B. Fincher, Thomas Shafee, Antony Bacic, Jochen Zimmer, Xiaohui Xing, Vincent Bulone, Monika S. Doblin, Eric M. Roberts

Research output: Contribution to journalArticlepeer-review

Abstract

Linear, unbranched (1,3;1,4)-β-glucans (mixed-linkage glucans or MLGs) are commonly found in the cell walls of grasses, but have also been detected in basal land plants, algae, fungi and bacteria. Here we show that two family GT2 glycosyltransferases from the Gram-positive bacterium Sarcina ventriculi are capable of synthesizing MLGs. Immunotransmission electron microscopy demonstrates that MLG is secreted as an exopolysaccharide, where it may play a role in organizing individual cells into packets that are characteristic of Sarcina species. Heterologous expression of these two genes shows that they are capable of producing MLGs in planta, including an MLG that is chemically identical to the MLG secreted from S. ventriculi cells but which has regularly spaced (1,3)-β-linkages in a structure not reported previously for MLGs. The tandemly arranged, paralogous pair of genes are designated SvBmlgs1 and SvBmlgs2. The data indicate that MLG synthases have evolved different enzymic mechanisms for the incorporation of (1,3)-β- and (1,4)-β-glucosyl residues into a single polysaccharide chain. Amino acid variants associated with the evolutionary switch from (1,4)-β-glucan (cellulose) to MLG synthesis have been identified in the active site regions of the enzymes. The presence of MLG synthesis in bacteria could prove valuable for large-scale production of MLG for medical, food and beverage applications.

Original languageEnglish
Pages (from-to)1245-1261
Number of pages17
JournalMOLECULAR MICROBIOLOGY
Volume121
Issue number6
DOIs
Publication statusPublished - Jun 2024
Externally publishedYes

Keywords

  • (1,3;1,4)-β-glucan synthase
  • c-di-GMP binding motif
  • gram-positive bacteria
  • heterologous expression
  • mixed-linkage glucan
  • polysaccharide biosynthesis

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