MS08-P02 Structural insight into protein-aided bacterial biofilm formationMicroorganisms form surface-attached communities, termed biofilms, which can serve as protection against host immune reactions or antibiotics. Bacillus subtilis biofilms contain TasA as major proteinaceous component in addition to exopolysaccharides. In stark contrast to the initially unfolded biofilm proteins of other bacteria, TasA is a soluble, stably folded monomer, whose structure we have determined by X-ray crystallography.
In this work, we present a high-resolution crystal structure of soluble, monomeric TasA in its mature secreted form. Despite its apparent homology to camelysins, biochemical experiments suggest that TasA is not an active protease. As a basis for understanding the structural changes occurring during fiber and biofilm formation, the monomer and multimeric forms were investigated in vitro and in vivo by NMR, analytical ultracentrifugation (AUC), and other biophysical techniques. In particular, we analyzed in vitro the transformation of soluble monomeric TasA into two different states, a gel-like form and fibrils. Magic-angle spinning (MAS) NMR applied to biofilms that were generated by adding soluble, monomeric and isotope-labeled TasA to the medium of B. subtilis ΔtasA cultures allowed probing of the in vivo situation, revealing the formation of homogeneous TasA fibers as the major proteinaceous extracellular matrix component. Thereby, we characterized the transition of folded TasA into fibrils, both in vitro and in its natural biofilm environment on a molecular level.
Understanding the formation and structure of protective bacterial biofilms will help to design and identify antimicrobial strategies. Our experiments with the secreted major biofilm protein TasA characterize on a molecular level in vivo the transition of a folded protein into protease-resistant biofilm-stabilizing fibrils. Such conformational changes from a globular state into fibrillar structures are so far not seen for other biofilm-forming proteins. In this context, TasA can serve as a model system to study functional fibril formation from a globular state.
Diehl A, Roske Y, Ball L, Chowdhury A, Hiller M, Molière N, Kramer R, Stöppler D, Worth CL, Schlegel B, Leidert M, Cremer N, Erdmann N, Lopez D, Stephanowitz H, Krause E, van Rossum BJ, Schmieder P, Heinemann U, Turgay K, Akbey Ü, Oschkinat H. (2018) Proc Natl Acad Sci U S A. 115 (13), 3237-3242
Romero D, Aguilar C, Losick R, Kolter R. (2010) Proc Natl Acad Sci U S A. 107 (5), 2230-4.
Stöver AG, Driks A. (1999) J Bacteriol. 181(5), 1664-72.Keywords: TasA, structure, biofilm