Molecular architecture of bacterial amyloids in Bacillus biofilms

Abstract

The formation of biofilms provides structural and adaptive bacterial response to the environment. In Bacillus species, the biofilm extracellular matrix is composed of exopolysaccharides, hydrophobins, and several functional amyloid proteins. We report, using multiscale approaches such as solid‐state NMR (SSNMR), electron microscopy, X‐ray diffraction, dynamic light scattering, attenuated total reflection Fourier transform infrared (FTIR), and immune‐gold labeling, the molecular architecture of B. subtilis and pathogenic B. cereus functional amyloids. SSNMR data reveal that the major amyloid component TasA in its fibrillar amyloid form contain β‐sheet and α‐helical secondary structure, suggesting a nontypical amyloid architecture in B. subtilis. Proteinase K digestion experiments indicate the amyloid moiety is ~100 aa long, and subsequent SSNMR and FTIR signatures for B. subtilis and B. cereus TasA filaments highlight a conserved amyloid fold, albeit with substantial differences in structural polymorphism and secondary structure composition. Structural analysis and coassembly data on the accessory protein TapA in B. subtilis and its counterpart camelysin in B. cereus reveal a catalyzing effect between the functional amyloid proteins and a common structural architecture, suggesting a coassembly in the context of biofilm formation. Our findings highlight nontypical amyloid behavior of these bacterial functional amyloids, underlining structural variations between biofilms even in closely related bacterial species.—El Mammeri, N., Hierrezuelo, J., Tolchard, J., Cámara‐Almirón, J., Caro‐Astorga, J., Álvarez‐Mena, A., Dutour, A., Berbon, M., Shenoy, J., Morvan, E., Grélard, A., Kauffmann, B., Lecomte, S., de Vicente, A., Habenstein, B., Romero, D., Loquet, A. Molecular architecture of bacterial amyloids in Bacillus biofilms. FASEB J. 33, 12146‐12163 (2019). http://www.fasebj.org

The majority of the matrix protein TapA is dispensable for Bacillus subtilis colony biofilm architecture

“…subtilis depends on the protein TapA, which has a role in promoting TasA stability and fibre formation in vivo (Branda et al, 2006;Romero et al, 2010;Romero et al, 2014;Abbasi et al, 2019;El Mammeri et al, 2019 Figure 3f) and recent NMR analysis has suggested that the C-terminus of TapA is a disordered protein, while the N-terminus is a structured domain, with the two domains interacting with lipid vesicles in a co-operative manner (Abbasi et al, 2019). Collectively, our immunoblot and genetic data support the conclusion that TapA is cleaved at two positions.…”

“…Secondary structure analysis revealed TapA to be a two‐domain protein with significant regions of disorder (Abbasi et al ., 2019). Additionally TapA has recently been shown to form fibres (El Mammeri et al ., 2019). The absence of TapA is correlated with a reduction in the level of TasA in the biofilm matrix (Romero et al ., 2014).…”

Artificial Sporulation Induction (ASI) by kinA Overexpression Affects the Proteomes and Properties of Bacillus subtilis Spores

“…Two proteins are affected in the comparison of WT+/− spores ( Supplementary Figure S2A ). YhzC, a functionally unknown protein, is downregulated, and TasA, the major component of biofilm matrix [ 20 ], is upregulated.…”

Molecular structure and interactions within amyloid-like fibrils formed by a low-complexity protein sequence from FUS

“…Hydrophobic interactions and salt bridges can also be important stabilizing interactions for pathogenic amyloid fibrils, as indicated by structural studies of amyloid-β 50,54,61,62 and αsynuclein 51,63 fibrils, as well as for functional amyloids [64][65][66] . The absence of charged amino acid side chains and the absence of purely hydrophobic residues other than Pro within the FUS-LC-C fibril core implies that hydrophobic interactions and salt bridges do not account for the formation of FUS-LC-C fibrils.…”