|Nava Segev, PhD
UIC Biological Sciences, 4120 MBRB M/C 567
900 South Ashland Ave.
Chicago, IL 60607
Office: (312) 355-0142
Lab: (312) 413-2471
Fax: (312) 413-2691
Molecular switches and cascades regulating protein traffic in yeast
Interaction of cells with their environment is crucial for all cellular and systemic functions. This interaction is dependent on the secretory pathway through which proteins and peptides are secreted; receptors, ion channels and ion pumps are presented on the plasma membrane; and ligands and receptors are internalized. In the secretory pathway proteins are transported between intracellular compartments via membranous vesicles. GTPases play a key role in the regulation of this vesicular trafficking. The mechanisms and machinery that underlie vesicle formation and targeting have been unraveled in the last decade and were found to be highly conserved between yeast and man. Our long term goal is to understand how vesicular transport operates, to elucidate novel mechanisms that coordinate the different steps of the secretory pathway, and the specific role(s) that Ypt/Rab GTPases have in this regulation. We are using yeast as a model system to address these complicated issues, since it is allows the use of genetic approaches in addition to molecular and cellular methods.
Our research focuses on proteins that interact with exocytic Ypt GTPases and the mechanisms by which they function as effectors or regulators. We are performing a genome-wide screen using biochemical genomics to identify proteins that interact with exocytic Ypt GTPases. Existing as well as newly identified genes are examined for their role in protein transport by analyzing potential secretory defects in mutants, and studying intracellular localization of their products. These genes are being used to address the following questions: 1) What role do regulators of Ypt nucleotide cycling play in Ypt-mediated protein transport? Cycling between the GTP- and GDP-bound forms, facilitated by accessory factors, is considered crucial for Ypt/Rab function. However, little is known regarding how these factors find their Ypt/Rab target or how they facilitate nucleotide exchange and hydrolysis. To resolve issues concerning their specificity and mechanism of action, their interaction with Ypt and other proteins that function in secretion is examined in vivo and in vitro. 2) What role do effectors of Ypt GTPases play in protein transport? Ypt/Rab proteins, like other ras-related GTPases, are believed to function through the regulation of down-stream effectors in a GTP-dependent manner, to transmit a signal from the GTP-bound form to the membrane docking and/or fusion apparatus. To determine the exact mechanism by which Ypt effectors function, we are studying the behavior of mutations in these genes in vesicle budding, targeting, or fusion, and the nature of their interaction with Ypt GTPases. Finally, we are exploring the exciting possibility that Ypt proteins function in GTPase cascades that coordinate the different steps of the secretory pathway.
Tokarev AA, Taussig D, Sundaram G, Lipatova Z, Liang Y, Mulholland JW and Segev N (2009) TRAPP II complex assembly requires Trs33 or Trs65. Traffic (epub ahead of print).
Sacher M, Kim YG, Lavie A, Oh BH and Segev N (2008) The TRAPP complex: insights into its architecture and function. Traffic 9: 2032-2042.
Lipatova Z, Tokarev AA, Jin Y, Mulholland J, Weisman L and Segev N (2008) Direct interaction between a myosin V motor and the Rab GTPases Ypt31/32 is required for polarized secretion. Mol Biol Cell 19: 4177-4187.
Liang Y, Morozova N, Tokarev AA, Mulholland JW and Segev N (2007) The role of Trs65 in the Ypt/Rab guanine nucleotide exchange factor function TRAPP II complex. Mol Biol Cell 18: 2533-2541.
Morozova N, Liang Y, Tokarev A, Chen S, Cox R, Andrejic J, Lipatova Z, Sciora V, Emr S and Segev N (2006) TRAPP II subunits are required for the specificity switch of a dual-Ypt/Rab GEF. Nature Cell Biol 8: 1263-1269 (Highlighted in Nature Reviews Mol Cell Biol 7:881).
Chen SH, Chen S, Tokarev A, Liu F, Jedd G and Segev N (2005) Ypt31/32, and their novel F-Box effector protein, Rcy1, regulate protein recycling. Mol Biol Cell 16:178-192.
Segev N (2001) Ypt and Rab GTPases: Insight into functions through novel interactions. Curr Opin Cell Biol 13:500-511.