The role of the TtpC protein in energy transduction in the TonB2 systems of pathogenic vibrois

Iron acquisition is essential for bacterial survival, and Gram‑negative species rely on the TonB‑ExbB‑ExbD system to transfer energy from the inner membrane to outer‑membrane iron‑siderophore transporters. Unlike E. coli, Vibrio species possess multiple TonB systems that include an additional protein, TtpC, which is required for energy transduction and iron uptake. TtpC shares a conserved SxxxH motif—absent in Vibrio TonB2 but essential for Fe‑ferrichrome transport—supporting its role as the primary energy‑transducing component. These findings reveal a unique four‑protein TonB2 system in Vibrio, indicating a more complex, specialized mechanism of energy transduction used by marine bacteria.