Abstract
Growth of the cholera bacterium Vibrio cholerae in a biofilm community contributes to both its pathogenicity and survival in aquatic environmental niches. The major components of V. cholerae biofilms include Vibriopolysaccharide (VPS) and the extracellular matrix proteins RbmA, RbmC, and Bap1. To further elucidate the previously observed overlapping roles of Bap1 and RbmC in biofilm architecture and surface attachment, here we investigated the structural and functional properties of Bap1. Soluble expression of Bap1 was possible only after the removal of an internal 57-amino-acid-long hydrophobic insertion sequence. The crystal structure of Bap1 at 1.9 Å resolution revealed a two-domain assembly made up of an eight-bladed β-propeller interrupted by a β-prism domain. The structure also revealed metal-binding sites within canonical calcium blade motifs, which appear to have structural rather than functional roles. Contrary to results previously observed with RbmC, the Bap1 β-prism domain did not exhibit affinity for complex N-glycans, suggesting an altered role of this domain in biofilm-surface adhesion. Native polyacrylamide gel shift analysis did suggest that Bap1 exhibits lectin activity with a preference for anionic or linear polysaccharides. Our results suggest a model for V. cholerae biofilms in which Bap1 and RbmC play dominant but differing adhesive roles in biofilms, allowing bacterial attachment to diverse environmental or host surfaces.
Highlights
Growth of the cholera bacterium Vibrio cholerae in a biofilm community contributes to both its pathogenicity and survival in aquatic environmental niches
Our results suggest a model for V. cholerae biofilms in which Bap1 and RbmC play dominant but differing adhesive roles in biofilms, allowing bacterial attachment to diverse environmental or host surfaces
We report the 1.9 Å crystal structure of the V. cholerae biofilm matrix protein Bap1⌬57 and demonstrate that the Bap1⌬57 -prism domain displays a sugar-binding profile that differs from other V. cholerae -prism domains (RbmC and V. cholerae cytolysin (VCC)), with putative specificity for anionic polysaccharides and/or polysaccharides with a linear backbone
Summary
Growth of the cholera bacterium Vibrio cholerae in a biofilm community contributes to both its pathogenicity and survival in aquatic environmental niches. The major components of V. cholerae biofilms include Vibrio polysaccharide (VPS) and the extracellular matrix proteins RbmA, RbmC, and Bap. The major components of the V. cholerae biofilm matrix are Vibrio polysaccharide (VPS), nucleic acids, and the matrix proteins RbmA, RbmC, and Bap1 [3, 8, 9]. EDITORS’ PICK: Bap biofilm matrix protein from V. cholerae rugose background suggest that Bap and RbmC have similar, additive, and essential roles in biofilm formation [14]. Further analysis of the V. cholerae biofilm architecture using microscopy techniques provides additional insight implicating RbmA in V. cholerae cell– cell adhesion, Bap in surface attachment, and both Bap and RbmC in formation of dynamic envelopes that encase clusters of cells in the mature biofilm [9]. Our results provide a starting point for understanding how Bap and RbmC may participate in structural and adhesive roles in building the V. cholerae biofilm matrix
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