Pathways & interactions
RTX secretion protein D, Gram-negative bacteria (IPR003997)
Short name: Rtx_secretion_protD_GmN_bac
Overlapping homologous superfamilies
- RND efflux pump, membrane fusion protein (IPR006143)
- RTX secretion protein D, Gram-negative bacteria (IPR003997)
Secretion of virulence factors in Gram-negative bacteria involves transportation of the protein across two membranes to reach the cell exterior [PMID: 1558765]. Four principal exotoxin secretion systems have been described. In the type II and IV secretion systems, toxins are first exported to the periplasm by way of a cleaved N-terminal signal sequence; a second set of proteins is used for extracellular transport (type II), or the C terminus of the exotoxin itself is used (type IV). Type III secretion involves at least 20 molecules that assemble into a needle; effector proteins are then translocated through this without need of a signal sequence. In the Type I system, a complete channel is formed through both membranes, and the secretion signal is carried on the C terminus of the exotoxin.
The RTX (repeats in toxin) family of cytolytic toxins belong to the Type I secretion system, and are important virulence factors in Gram-negative bacteria. As well as the C-terminal signal sequence, several glycine-rich repeats are also found. These are essential for binding calcium, and are critical for the biological activity of the secreted toxins [PMID: 8800842]. All RTX toxin operons exist in the order rtxCABD, RtxA protein being the structural component of the exotoxin, both RtxB and D being required for its export from the bacterial cell; RtxC is an acyl-carrier-protein-dependent acyl- modification enzyme, required to convert RtxA to its active form [PMID: 10470043].
Escherichia coli haemolysin (HlyA) is often quoted as the model for RTX toxins. Recent work on its relative rtxC gene product HlyC [PMID: 9521785] has revealed that it provides the acylation aspect for post-translational modification of two internal lysine residues in the HlyA protein. HlyD provides a cytoplasmic transport moiety for HlyA, and is situated in both the cytoplasm and periplasm, having a single transmembrane segment [PMID: 1495479].
- PR01490 (RTXTOXIND)