STRUCTURE-FUNCTION OF THE ACTIN CYTOSKELETON

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The actin cytoskeleton plays an essential role in multiple cellular functions, including cytokinesis, vesicular trafficking and the maintenance of cell shape and polarity. The driving force for these processes is the dynamic remodeling of the actin cytoskeleton into supramolecular functional networks, a process that is a tightly regulated in the cell and involves hundreds of actin-binding and signaling proteins. A number of projects in our lab aim to understand the molecular mechanisms of actin cytoskeleton dynamics. Some of these projects involve SAXS/WAXS data collection at BioCAT, including: Mechanism of actin filament nucleation by WH2 containing proteins. The WASP homology domain 2 (WH2) is an abundant actin-binding motif found in many proteins involved in actin filament nucleation and elongation. Based on our structures of WH2-actin (Chereau et al., PNAS 2005) we proposed that tandem WH2 domains line up actin subunits along a filament strand forming nuclei for actin assembly. To test this hypothesis we are working on the structures of actin minifilaments assembled via tandem WH2 domains constructs. Mechanism of actin filament nucleation by Arp2/3 complex. Arp2/3 complex, is an actin filament nucleation machinery, consisting of seven proteins, two of which are related to actin (Arp2 and Arp3). Arp2 and Arp3 are thought to form a trimeric polymerization seed together with an actin subunit bound to a WH2 domain of one of the many nucleation-promoting factor protein that activate Arp2/3, such as WASP. To understand the mechanism of filament nucleation by Arp2/3 complex, we are working on the structure of a 9 protein complex consisting of WASP + actin + Arp2/3-complex.