Vibrio MARTX toxin effectors in signaling and pathogenesis

Bacteria often coordinate secreted virulence factors to fine-tune the host response during infection. These coordinated events can include toxins counteracting or amplifying effects of another toxin. Multifunctional-autoprocessing repeats-in toxin (MARTX) toxins are large, secreted proteins that are a unique hybrids of secreted toxins and multi-effector delivery systems. Similar to many bacterial protein toxins, MARTX toxins are secreted from the bacteria and then form a pore in the host cell plasma membrane. After translocation of the central portion of the toxin, an autoprocessing cysteine protease domain is activated by binding inositol hexakisphosphate. CPD-mediated autoproteolysis of the large polypeptide results in release of the “MARTX effectors” to the cell cytosol, where they are free to move throughout the cell to access cellular targets and to exert their toxic effects. There are over 100 different bacterial taxa that carry a MARTX toxin. Across the different species, MARTX toxins carry up to 5 effector domains, selected from ten known effector domains. They have thus been called “cluster bombs”. An important feature of these toxins is that all the effectors linked together in a single polypeptide are delivered simultaneously to the same cell, at the same time, at equal equal stoichiometric ratio. While previous studies have employed a reductionist approach to determine the mechanism of action of individual effector domains, little is known about how these effector activities delivered together may act in synergy to promote infection. Further, due to horizontal gene transfer, the toxin repertoire can change frequently between strains of the same species, such that effector interplay could vary with each MARTX toxin variant. Thus, different strains within the same species may employ unique virulence strategies. In this renewal study, we will focus on how different combinations of the toxin signal together to enhance virulence. The study will focus on the actin crosslinking MARTX effector found in both Vibrio cholerae and Vibrio vulnificus can reprogram host cell signaling. We will further ask how other effectors co-delivered on the same toxin then complement or override this signaling program to optimally promote virulence. We will also expand this study into other larger MARTX toxins to explore how increasing the number of effectors can impact signal coordination to impact pathogenesis.