Abstract
The evolutionarily conserved protein, Arp2/3 complex (220 kDa), serves to nucleate rapid formation of branched actin filaments that promote cell motility and endocytosis. Our lab recently identified a novel negative regulator to this 3 mechanism: Syp1. Syp1 is thought to inhibit Las17, the yeast homologue of WASp family of Arp2/3 Nucleation Promoting Factors. Unlike other WASps, Las17 lacks auto-inhibition. To date, only two mild trans-inhibitors have been identified (Sla1 and Bbc1) and are thought to act cooperatively. Syp1 is the first protein shown to abolish Las17 activity completely. As a potent inhibitor, Syp1 is likely to play a major role on actin regulation, especially at the cortical patches where it localizes, and where endocytosis occurs. In this study, I characterized Syp1 's localization to the cortical actin patches in S. cerevisiae, investigated its recruitment, and specified its physical and functional interaction with Las17. My findings suggest that Syp1, in its native form, is in the same stable complex (of size ~ 275 kDa) with Las17. The two proteins, Syp1 and Las17, physically interact, but this interaction is not likely to be via Las17 proline-rich region. Syp1 localizes to cortical actin patches, and is recruited there by Clcl, an essential endocytic protein that appears early at the site of endocytosis. Recently, the importance of the linking between actin and endocytic machineries at the cortical actin patches has been emphasized by many studies, and Syp1 's appearance among the cast of proteins is exciting.