VibrioMARTX toxin processing and degradation of cellular Rab GTPases by the cytotoxic effector Makes Caterpillars Floppy

Abstract

Vibrio vulnificuscauses life threatening infections dependent upon the effectors released from the Multifunctional-Autoprocessing Repeats-In-Toxin (MARTX) toxin. The Makes Caterpillars Floppy-like (MCF) cysteine protease effector is activated by host ADP ribosylation factors (ARFs), although the targets of processing activity were unknown. In this study we show MCF binds Ras-related proteins in brain (Rab) GTPases at the same interface occupied by ARFs and then cleaves and/or degrades 24 distinct members of the Rab GTPases family. The cleavage occurs in the C-terminal tails of Rabs. We determine the crystal structure of MCF as a swapped dimer revealing the open, activated state of MCF and then use structure prediction algorithms to show that structural composition, rather than sequence or localization, determine Rabs selected as MCF proteolytic targets. Once cleaved, Rabs become dispersed in cells to drive organelle damage and cell death to promote pathogenesis of these rapidly fatal infections.

Structure and activation mechanism of the Makes caterpillars floppy 1 toxin

“…2). In addition, it is homologous to the Mcf-like domain of the multifunctional-autoprocessing repeats-in-toxin (MARTX) from Vibrio vulnificus, which induces cell apoptosis by cleaving C-terminal regions of Rab proteins 15 . We therefore named this domain protease effector domain (PED), reflecting its potential dual function.…”

“…Second, the central region of Mcf1 shares similarities with the 50 kDa Mcf-like effector domain of the multifunctional-autoprocessing repeats-in-toxin (MARTX) toxins of Vibrio vulnificus 13,14 . This domain is a cysteine protease that, upon autoproteolytic activation by host cell ADP-ribosylation factor (Arf) proteins, degrades Rab GTPases and induces cell apoptosis 15 . Third, Mcf1 possesses a highly hydrophobic sequence similar to that in the translocation region of the Clostridioides difficile toxin B (TcdB), suggesting that Mcf1 can undergo a conformational change and penetrate the endosomal membrane, similar to TcdB 16 .…”