The YeastGRD20Gene Is Required for Protein Sorting in thetrans-Golgi Network/Endosomal System and for Polarization of the Actin Cytoskeleton

Abstract

The proper localization of resident membrane proteins to the trans-Golgi network (TGN) involves mechanisms for both TGN retention and retrieval from post-TGN compartments. In this study we report identification of a new gene, GRD20, involved in protein sorting in the TGN/endosomal system of Saccharomyces cerevisiae. A strain carrying a transposon insertion allele of GRD20 exhibited rapid vacuolar degradation of the resident TGN endoprotease Kex2p and aberrantly secreted approximately 50% of the soluble vacuolar hydrolase carboxypeptidase Y. The Kex2p mislocalization and carboxypeptidase Y missorting phenotypes were exhibited rapidly after loss of Grd20p function in grd20 temperature-sensitive mutant strains, indicating that Grd20p plays a direct role in these processes. Surprisingly, little if any vacuolar degradation was observed for the TGN membrane proteins A-ALP and Vps10p, underscoring a difference in trafficking patterns for these proteins compared with that of Kex2p. A grd20 null mutant strain exhibited extremely slow growth and a defect in polarization of the actin cytoskeleton, and these two phenotypes were invariably linked in a collection of randomly mutagenized grd20 alleles. GRD20 encodes a hydrophilic protein that partially associates with the TGN. The discovery of GRD20 suggests a link between the cytoskeleton and function of the yeast TGN.

The yeast dynamin-related GTPase Vps1p functions in the organization of the actin cytoskeleton via interaction with Sla1p

“…These include Chc1p, Vps54p, Pik1p and Grd20p. Like the vps1 mutant, mutants of chc1, grd20 and vps54 all exhibited depolarization and aggregation of cortical actin patches at 37°C and, in the case of grd20, a significant delay in the turnover of the membrane receptor Ste3p (Spelbrink and Nothwehr, 1999;Walch-Solimena and Novick, 1999;Henry et al, 2002;Fiedler et al, 2002). The identification of Vps1p as a new factor from TGN to be required for normal actin organization further supports the connection between protein transport and actin cytoskeleton.…”

The conserved oligomeric Golgi complex acts in organ morphogenesis via glycosylation of an ADAM protease inC. elegans

“…The COG complex, also called the ldlCp complex, Sec34/Sec35p complex and GTC complex, has been identified independently by several groups working in both yeast and mammalian systems. The COG complex functions in multiple aspects of intracellular vesicle trafficking, including that between the endoplasmic reticulum (ER) and Golgi, between Golgi cisternae and from endosomes to Golgi (Krieger et al, 1981;Wuestehube et al, 1996;Walter et al, 1998;Spelbrink and Nothwehr, 1999;Whyte and Munro, 2001;Suvorova et al, 2002). Biochemical and electron microscopic analyses of the mammalian COG complex have identified eight protein components: COG-1-4 form lobe A of the complex, whereas COG-5-8 form lobe B (Ungar et al, 2002;Loh and Hong, 2004).…”

TheDrosophila Cog5Homologue Is Required for Cytokinesis, Cell Elongation, and Assembly of Specialized Golgi Architecture during Spermatogenesis

“…The eight-component mammalian conserved oligomeric Golgi (COG) complex and the homologous Sec34/35 complex in yeast have been proposed to assist in Golgi vesicle targeting VanRheenen et al, 1998;Walter et al, 1998;VanRheenen et al, 1999;Sacher et al, 2001;Whyte and Munro, 2001;Ungar et al, 2002). The COG complex can stimulate intra-Golgi trafficking in vitro (Walter et al, 1998), and subunits of the Sec34/35 complex have been shown to be required for ER-to-Golgi trafficking, retrograde transport through the Golgi, and trafficking between the Golgi and endosomes (Spelbrink and Nothwehr, 1999;VanRheenen et al, 1999;Whyte and Munro, 2001). However, a direct role of the COG complex in vesicle trafficking has not yet been demonstrated.…”