Structural and Biochemical Studies on PACSIN

PCH (pombe Cdc15 homology) family proteins are involved in endocytosis and cytokinesis. All PCH proteins possess a highly conserved F‐BAR domain at the N‐terminus and SH3 domain at the C‐terminus. The SH3 domain binds to dynamin, an essential component of vesicle dynamics, as well as WASP, a Rho GTPase effector that regulates actin assembly. And, the F‐BAR domain induces tubular membrane invaginations in cells, binds to microtubules and is responsible for the localization of the PCH protein at the plasma membrane. Mutations in the F‐BAR domain can lead to PAPA syndrome, an autoinflammatory disease. This poster describes biochemical and structural studies of mPACSIN2, a murine PCH family protein. Here we report the structure of F‐BAR domain of mPACSIN2 and the activation of WASP by full length mPACSIN2. As predicted from sequence analysis, the F‐BAR domain is distantly related to the BAR domain, a well‐known lipid binding module. Both the BAR and F‐BAR domains are constitutive dimers. The F‐BAR domain of mPACSIN2 is an S‐shaped dimer in contrast to crescent‐shaped dimer of BAR domain of dAmphiphysin. Both structures have coiled‐coils of three or more long kinked helices, forming a six‐bundle around the dimer interface. Helix 2 in mPACSIN2 is kinked and longer than the corresponding helix of the dAmphiphysin BAR domain. Full length mPACSIN2 can activate WASP in in vitro actin assembly assays, but the SH3 domain by itself cannot, indicating the influence of F‐BAR domain in modulating the activity of full length protein.