Colloidal-like aggregation of a functional amyloid protein

Abstract

Functional amyloid proteins are self-secreted by microbial cells that aggregate into extracellular networks and provide microbial colonies with mechanical stability and resistance to antibiotic treatment. In order to understand the...

Bacillus subtilis biofilm formation and social interactions

“…Unlike curli, the amyloid fibres that are produced by Escherichia coli and other enteric bacteria (reviewed elsewhere 23 ), monomeric TasA in B. subtilis is globular in solution and adopts a jelly-roll-like fold with a flexible helix-rich region 29 . At low pH, TasA forms dense gel-like networks that are comparable to colloidal aggregation 30 . Transmission electron microscopy (TEM) imaging of TasA fibres consistently reveals repeating units along the protofilament (smallest diameter fibres) axis that are estimated to be ~5 nm in length 22,28 , similar to the size of the TasA monomer.…”

Multiscale X-ray study of Bacillus subtilis biofilms reveals interlinked structural hierarchy and elemental heterogeneity

“…Facing the presence of cross beta sheet fingerprint in intact biofilms, its increase in the presence of TasA (in 24-and 72-hour WT samples) and in light of the literature debate on the amyloid nature of TasA (28,31,51,52), we were intrigued to learn more about the structure and composition of fibers formed in vitro from isolated TasA preparations. Recently, we have shown that TasA is polymorphic, as it forms fibers with different morphologies: aggregates in acidic solutions (termed 'aggregates' henceforth), thin and long fibers at high salt concentrations (termed 'fibrils' henceforth) and fiber bundles at high protein and salt concentration (henceforth termed' bundles') (30,53,54). A-C) XRF of TasA fibers, (A) formed in acidic conditions ('TasA aggregates), (B) high salt concentration ('TasA fibrils'), and (C) high protein and salt concentration ('TasA bundles').…”

“…Recently, we have shown that TasA is polymorphic, as it forms fibers with different morphologies: aggregates in acidic solutions (termed 'aggregates' henceforth), fiber bundles at high protein and salt concentration (termed 'bundles' henceforth) and thin and long fibers at high salt concentrations (termed 'fibrils' henceforth). 30,56,57 .…”

“…TasA aggregates: Purified TasA was passed through a HiLoad 26/60 Superdex S200 sizing column that was pre-equilibrated with a 50 mM NaCl and 5 mM HEPES solution at pH 8. The solution pH was then adjusted to 2.5 with formic acid, yielding TasA aggregates 56 and kept at room temperature for three days at 4 °C. The solution was exchanged by consecutive centrifugation (5000 rpm, 10 min) and supernatant replacement with TDW, three times every 24 h. The solution was then lyophilized and placed between two silicon nitride membranes or resuspended in a drop of water and mounted on a loop (Hampton Research).…”

“…We were therefore intrigued to compare the structure of fibers formed in vitro from isolated TasA preparations with the general structural features of the ECM in intact biofilms. Recently, we have shown that TasA is polymorphic, as it forms fibers with different morphologies: aggregates in acidic solutions (termed 'aggregates' henceforth), fiber bundles at high protein and salt concentration (termed 'bundles' henceforth) and thin and long fibrils at high salt concentrations (termed 'fibrils' henceforth) (36,52,53). Fig.…”