Toxin-membrane interactions are poorly understood on the molecular level due tothe inherent difficulty of crystallizing membrane protein complexes and the large size (>50 kDa) of most functional AB or MARTX protein toxins. Toxins can interact with membranes at three stages during intoxication: 1) receptor binding to the cell surface, 2) membrane translocation, and/or 3) intracellular membrane targeting. To understand the intoxication process, it is necessary to develop an understanding of the structures, dynamics, and mechanisms through which toxins interact with membranes.In this thesis, we focus on the membrane-binding domains of Pasteurella multocida toxin, a 144-kDa dermonecrotic AB-type toxin that causes atrophic rhinitis, and homologous domains in other toxins. We address both the N-terminal domain necessary for receptor-mediated endocytosis into the cell, as well as the intracellular membrane localization domain (MLD), which is believed to be necessary to enable proper targeting of the catalytic domain for cytotoxicity.We demonstrate that the N-terminal receptor-binding domain preferentially binds to the membrane component sphingomyelin and a putative co-receptor (chapter 2), that the MLD undergoes a secondary-structure conformational change upon membrane interaction (chapter 3), and that this phenomenon has pH-dependent dynamics that may enable the MLD to survive the endosome before it becomes functional at cytosolic pH (chapter 4). This thesis provides a framework for understanding the topology and chemistry behind toxin-membrane interactions.
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Toxin-membrane interactions of Pasteurella multocida toxin and homologous domains
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