The Bacterial Extracellular Matrix Protein TapA Is a Two‐Domain Partially Disordered Protein

Abstract

Biofilms are aggregates of microbial cells that form on surfaces and at interfaces, and are encased in an extracellular matrix. In biofilms made by the soil bacterium Bacillus subtilis, the protein TapA mediates the assembly of the functional amyloid protein TasA into extracellular fibers, and it anchors these fibers to the cell surface. We used circular dichroism and NMR spectroscopy to show that, unlike the structured TasA, TapA is disordered. In addition, TapA is composed of two weakly interacting domains: a disordered C‐terminal domain and a more structured N‐terminal domain. These two domains also exhibited different structural changes in response to changes in external conditions, such as increased temperatures and the presence of lipid vesicles. Although the two TapA domains weakly interacted in solution, their cooperative interaction with lipid vesicles prevented disruption of the vesicles. These findings therefore suggest that the two‐domain composition of TapA is important in its interaction with single or multiple partners in the extracellular matrix in biofilms.

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.…”

“…TapA is described as an accessory protein that is thought to be needed for the formation of TasA fibres (Romero et al ., 2010; Romero et al ., 2011), and more specifically, for the attachment of the TasA fibres to the cell surface. 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).…”

Computational investigation for modelling the protein-protein interaction of TasA(28-261)– TapA(33-253): a decisive process in biofilm formation byBacillus subtilis

“…This observation is consistent with the recent report which described TapA to be composed of two interacting domains; a disordered C-terminal domain and a more structured N-terminal domain(Abbasi et al, 2018). Noticeably, the two-domain composition of TapA has been suggested to be important for its interactions in the extracellular matrix in biofilms(Abbasi et al, 2018).…”

“…In the case of TapA 223 , the disordered region spreads in form of a single stretch from amino acid residues 200-251 (Supplementary Fig S2A & S2B). Again, these results were consistent with the report describing the disordered domain close to C-terminus in case of TapA(Abbasi et al, 2018).…”

Dual functionality of the TasA amyloid protein inBacillusphysiology and fitness on the phylloplane

“…Indeed, our results are supported by evidence that TasA can preferentially interact with model bacterial membranes, which affects fiber assembly 83 , and that TasA fibers are located and attached to the cell surface via a proposed interaction with TapA, which forms foci that seem to be present on the cell wall 76 . Interestingly, TapA has been recently characterized as a two-domain, partially disordered protein 84 . Disordered domains can be flexible enough to interact with multiple partners 85, 86 , suggesting a similar mechanism for TapA: the N-terminal domain might be involved in the interaction with other protein partners, whereas the C-terminal disordered domain might anchor the protein to the cell surface.…”