| Summary: | <p>MACPF/CDCs are an ancient superfamily of pore forming proteins that have evolved a critical role in both cellular defence and attack. Many copies of MACPF/CDC proteins are released by a cell before binding to target membranes, oligomerising and undergoing a large structural rearrangement to punch a hole into the membrane, typically killing the target cell. In this thesis the steps of pore formation from membrane recognition through to oligomerisation and membrane insertion have been investigated for several recently discovered MACPF/CDC proteins using a combination of structural and computational biology techniques.</p>
<p>Perforin-like proteins (PLPs) belong to the MACPF/CDC superfamily and are unique to apicomplexan parasites including Plasmodium and Toxoplasma. PLPs have a role in facilitating parasite escape from host cells following replication, however their precise mechanism of action is unknown. </p>
<p>Here, molecular simulation approaches were used to investigate the stages of pore formation of the Toxoplasma gondii PLP1 (TgPLP1). The mode of membrane binding of TgPLP1 was determined, while investigation of oligomerisation states of the MACPF domain led to the generation of a model for the TgPLP1 transmembrane pore structure. Plasmodium have 5 PLPs (PPLPs1-5), which are expressed at different points in their lifecycles. The crystal structure of the Plasmodium PLP1 APC domain is presented here, and molecular dynamics (MD) was used to investigate PPLP1 and PPLP2 membrane binding, showing that these proteins have distinct mechanisms of membrane binding. </p>
<p>Another recently discovered MACPF/CDC protein is perforin-2, a close relative to perforin, which is produced by both immune and parenchymal cells in the body to defend against intracellular bacteria. The structures of the perforin-2 monomer and pre-pore were recently solved, and here we used MD to investigate the initial steps of membrane recognition and oligomerisation of perforin-2. A key finding was that perforin-2 binds to the membrane with its MACPF domain facing away from the bilayer, therefore identifying a unique mechanism of binding and activation amongst the MACPF/CDC family.</p>
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