4zdw
From Proteopedia
Crystal structure of the Rab GTPase Sec4p mutant - S29V in complex with Sec2p and GDP
Structural highlights
Function[SEC4_YEAST] Involved in exocytosis. Maybe by regulating the binding and fusion of secretory vesicles with the cell surface. The GTP-bound form of SEC4 may interact with an effector, thereby stimulating its activity and leading to exocytotic fusion. SEC4 may be an upstream activator of the 19.5S SEC8/SEC15 particle. SEC4 probably interacts directly with SEC8; it could serve as the attachment site for the SEC8/SEC15 particle.[1] [SEC2_YEAST] Guanine nucleotide exchange factor for SEC4, catalyzing the dissociation of GDP from SEC4 and also potently promoting binding of GTP. Activation of SEC4 by SEC2 is needed for the directed transport of vesicles to sites of exocytosis. Binds the Rab GTPase YPT32, but does not have exhange activity on YPT32.[2] [3] [4] Publication Abstract from PubMedBACKGROUND: Sec4p is a small monomeric Ras-related GTP-binding protein (23 kDa) that regulates polarized exocytosis in S. cerevisiae. In this study we examine the structural effects of a conserved serine residue in the P-loop corresponding to G12 in Ras. RESULTS: We show that the Sec4p residue serine 29 forms a hydrogen bond with the nucleotide. Mutations of this residue have a different impact than equivalent mutations in Ras and can form stable associations with the exchange factor allowing us to elucidate the structure of a complex of Sec4p bound to the exchange factor Sec2p representing an early stage of the exchange reaction. CONCLUSIONS: Our structural investigation of the Sec4p-Sec2p complex reveals the role of the Sec2p coiled-coil domain in facilitating the fast kinetics of the exchange reaction. For Ras-family GTPases, single point mutations that impact the signaling state of the molecule have been well described however less structural information is available for equivalent mutations in the case of Rab proteins. Understanding the structural properties of mutants such as the one described here, provides useful insights into unique aspects of Rab GTPase function. New insights into the molecular mechanism of the Rab GTPase Sec4p activation.,Rinaldi FC, Packer M, Collins R BMC Struct Biol. 2015 Aug 12;15:14. doi: 10.1186/s12900-015-0041-5. PMID:26263895[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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