Peptidoglycan-binding protein TsaP functions in surface assembly of type IV pili

Abstract

Type IV pili (T4P) are ubiquitous and versatile bacterial cell surface structures involved in adhesion to host cells, biofilm formation, motility, and DNA uptake. In Gram-negative bacteria, T4P pass the outer membrane (OM) through the large, oligomeric, ring-shaped secretin complex. In the β-proteobacterium Neisseria gonorrhoeae, the native PilQ secretin ring embedded in OM sheets is surrounded by an additional peripheral structure, consisting of a peripheral ring and seven extending spikes. To unravel proteins important for formation of this additional structure, we identified proteins that are present with PilQ in the OM. One such protein, which we name T4P secretin-associated protein (TsaP), was identified as a phylogenetically widely conserved component of the secretin complex that co-occurs with genes for T4P in Gram-negative bacteria. TsaP contains an N-terminal carbohydrate-binding lysin motif (LysM) domain and a C-terminal domain of unknown function. In N. gonorrhoeae, lack of TsaP results in the formation of membrane protrusions containing multiple T4P, concomitant with reduced formation of surface-exposed T4P. Lack of TsaP did not affect the oligomeric state of PilQ, but resulted in loss of the peripheral structure around the PilQ secretin. TsaP binds peptidoglycan and associates strongly with the OM in a PilQ-dependent manner. In the δ-proteobacterium Myxococcus xanthus, TsaP is also important for surface assembly of T4P, and it accumulates and localizes in a PilQ-dependent manner to the cell poles. Our results show that TsaP is a novel protein associated with T4P function and suggest that TsaP functions to anchor the secretin complex to the peptidoglycan.

Architecture of the type IVa pilus machine

“…Ten highly conserved proteins are known to constitute the T4PM (16, 17). PilA, the major pilin protein, contains an N-terminal hydrophobic α helix and alternates between being anchored individually in the IM or bundled with other PilA N-terminal α helices to form the central pilus core (18).…”

Esx Systems and the Mycobacterial Cell Envelope: What's the Connection?

“…Peptidoglycan-binding proteins promote pilus assembly and anchoring in the cell envelope. In the Neisseria gonorrhoeae type IVa pilus system, a peptidoglycan-binding protein anchors the apparatus in the membrane (153). In the Pseudomonas aeruginosa type IV pilus system FimV, an inner membrane protein that binds peptidoglycan is required for multimerization of PilQ (outer membrane component of the type VI pilus [154]).…”

Not just an antibiotic target: Exploring the role of type I signal peptidase in bacterial virulence

“…178 In the case of type IV pili, TsaP is another component of the OM pore that is likely dependent on SPase processing. 179 Depending on the specific organism, the secretin of the T2SS may rely on the type II signal peptidase for processing. 180–182 …”