TCPa

tcpA is a gene in Vibrio cholerae that encodes the major pilin subunit of the toxin-coregulated pilus (TCP). TCP is a surface filament of the type IV pilus family that mediates adherence to intestinal mucosa and is essential for efficient colonization during infection. The TcpA pilus is assembled by the bacterium's type IV pilus assembly machinery and forms the filamentous projection used in attachment and microcolony formation.

Genetic organization: tcpA is part of the tcp operon, which includes genes involved in pilus assembly and regulation. Expression of tcpA is controlled by the ToxR regulon: environmental signals activate ToxR/ToxS, which induce regulators such as TcpP/TcpH, leading to expression of toxT, which activates tcpA and ctxAB (cholera toxin).

Functional significance: TCP serves as a key colonization factor and is required for efficient intestinal colonization and virulence in V. cholerae. Additionally, TCP serves as the receptor for CTXΦ, a filamentous phage that carries the cholera toxin genes; acquisition of CTXΦ by TCP-bearing strains spreads virulence.

Evolution and significance: tcpA and the TCP operon are conserved in toxigenic V. cholerae strains and have homologs in related Vibrio species, reflecting a shared mechanism of host colonization. TcpA has been explored as a target for vaccines and diagnostics due to its surface exposure and role in adherence.