This is a membrane localization domain found in multiple families of bacterial toxins including all of the clostridial glucosyltransferase toxins and various MARTX toxins (multifunctional-autoprocessing RTX toxins) [1,4]. In the Pasteurella multocida toxin (PMT) C-terminal fragment, structural analysis have indicated that the C1 domain possesses a signal that leads the toxin to the cell membrane. Furthermore, the C1 domain was found to structurally resemble the phospholipid-binding domain of C. difficile toxin B [2]. Functional studies in Vibrio cholera indicate that the subdomain at the N terminus of RID (Rho-inactivation domain), homologous to the membrane targeting C1 domain of Pasteurella multocida toxin, is a conserved membrane localization domain essential for proper localization [1]. The Rho-inactivation domain (RID) of MARTX (Multifunctional Autoprocessing RTX toxin) is responsible for inactivating the Rho-family of small GTPases in Vibrio cholerae. It is a bacterial toxin that self-process by a cysteine peptidase mechanism [3]. The Vibrio cholerae RTX toxin is an autoprocessing cysteine protease whose activity is stimulated by the intracellular environment [3]. This cysteine peptidase belongs to MEROPS peptidase family G6.

1: Identification of a conserved membrane localization domain within numerous large bacterial protein toxins. Geissler B, Tungekar R, Satchell KJ; Proc Natl Acad Sci U S A. 2010;107:5581-5586. PMID:20212166

2: Crystal structures reveal a thiol protease-like catalytic triad in the C-terminal region of Pasteurella multocida toxin. Kitadokoro K, Kamitani S, Miyazawa M, Hanajima-Ozawa M, Fukui A, Miyake M, Horiguchi Y; Proc Natl Acad Sci U S A. 2007;104:5139-5144. PMID:17360394

3: Autoprocessing of the Vibrio cholerae RTX toxin by the cysteine protease domain. Sheahan KL, Cordero CL, Satchell KJ; EMBO J. 2007;26:2552-2561. PMID:17464284

4: The bacterial Ras/Rap1 site-specific endopeptidase RRSP cleaves Ras through an atypical mechanism to disrupt Ras-ERK signaling. Biancucci M, Minasov G, Banerjee A, Herrera A, Woida PJ, Kieffer MB, Bindu L, Abreu-Blanco M, Anderson WF, Gaponenko V, Stephen AG, Holderfield M, Satchell KJF; Sci Signal. 2018; [Epub ahead of print] PMID:30279169