Yeast Irc6p is a novel type of conserved clathrin coat accessory factor related to small G proteins |
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| Authors: | Sabine Gorynia Todd C Lorenz Giancarlo Costaguta Lydia Daboussi Duilio Cascio Gregory S Payne |
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| Institution: | University of Chicago;aDepartment of Biological Chemistry, School of Medicine, University of California at Los Angeles, Los Angeles, CA 90095;bMolecular Biology Institute, University of California at Los Angeles, Los Angeles, CA 90095;cDepartment of Energy Institute of Genomics and Proteomics, University of California at Los Angeles, Los Angeles, CA 90095 |
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| Abstract: | Clathrin coat accessory proteins play key roles in transport mediated by clathrin-coated vesicles. Yeast Irc6p and the related mammalian p34 are putative clathrin accessory proteins that interact with clathrin adaptor complexes. We present evidence that Irc6p functions in clathrin-mediated traffic between the trans-Golgi network and endosomes, linking clathrin adaptor complex AP-1 and the Rab GTPase Ypt31p. The crystal structure of the Irc6p N-terminal domain revealed a G-protein fold most related to small G proteins of the Rab and Arf families. However, Irc6p lacks G-protein signature motifs and high-affinity GTP binding. Also, mutant Irc6p lacking candidate GTP-binding residues retained function. Mammalian p34 rescued growth defects in irc6∆ cells, indicating functional conservation, and modeling predicted a similar N-terminal fold in p34. Irc6p and p34 also contain functionally conserved C-terminal regions. Irc6p/p34-related proteins with the same two-part architecture are encoded in genomes of species as diverse as plants and humans. Together these results define Irc6p/p34 as a novel type of conserved clathrin accessory protein and founding members of a new G protein–like family. |
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