Cog1p Plays a Central Role in the Organization of the Yeast Conserved Oligomeric Golgi Complex

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The conserved oligomeric Golgi (COG) complex is required, along with SNARE and Sec1/Munc18 (SM) proteins, for vesicle docking and fusion at the Golgi. COG, like other multisubunit tethering complexes (MTCs), is thought to function as a scaffold and/or chaperone to direct the assembly of productive SNARE complexes at the sites of membrane fusion. Reflecting this essential role, mutations in the COG complex can cause congenital disorders of glycosylation. A deeper understanding of COG function and dysfunction will likely depend on elucidating its molecular structure. Despite some progress toward this goal, including EM studies of COG lobe A (subunits 1-4) and higher-resolution structures of portions of Cog2 and Cog4, the structures of COG's eight subunits and the principles governing their assembly are mostly unknown. Here, we report the crystal structure of a complex between two lobe B subunits, Cog5 and Cog7. The structure reveals that Cog5 is a member of the complexes associated with tethering containing helical rods (CATCHR) fold family, with homology to subunits of other MTCs including the Dsl1, exocyst, and Golgi-associated retrograde protein (GARP) complexes. The Cog5-Cog7 interaction is analyzed in relation to the Dsl1 complex, the only other CATCHR-family MTC for which subunit interactions have been characterized in detail. Biochemical and functional studies validate the physiological relevance of the observed Cog5-Cog7 interface, indicate that it is conserved from yeast to humans, and demonstrate that its disruption in human cells causes defects in trafficking and glycosylation.I n eukaryotes, the transport of proteins and lipids among intracellular compartments is mediated by vesicular and tubular carriers under the direction of an elaborate protein machinery (1). Among the most complex and least well-characterized components of this machinery are the multisubunit tethering complexes (MTCs) (2). MTCs are thought to mediate the initial attachment (or tethering) between a trafficking vesicle and its target membrane through a constellation of interactions (3, 4). These may include binding of the MTC to activated Rab GTPases, coiled-coil proteins such as Golgins, vesicle coat proteins, SNAREs, Sec1/ Munc18 (SM) proteins, and/or membrane lipids. Elucidating the 3D structures of MTCs represents an important step toward a better understanding of their molecular functions.Four of the known MTCs-termed complexes associated with tethering containing helical rods (CATCHR) or quatrefoil complexes (2, 5)-contain subunits whose shared 3D structure implies a single evolutionary progenitor (6-16). These CATCHR-family MTCs include the Dsl1, Golgi-associated retrograde protein (GARP), exocyst, and conserved oligomeric Golgi (COG) complexes, and they contain three, four, eight, and eight subunits, respectively. Although X-ray or NMR structures have been reported for 14 of these 23 subunits, only one of the structures contains the full-length polypeptide (14). Perhaps more critically, only two subunit interactions-both wit...

Section: Significancesupporting

confidence: 75%

“…1073/pnas.1414829111/-/DCSupplemental. cerevisiae Cog5 and Cog7 form an especially stable binary complex (22). Similarly, comprehensive in vitro cotranslation/coimmunoprecipitation experiments revealed that, among the eight human COG subunits, COG5 and COG7 were unusual in their ability to form a stable binary complex (23).…”

Section: Significancementioning

confidence: 99%

Cog5–Cog7 crystal structure reveals interactions essential for the function of a multisubunit tethering complex

Pokrovskaya

Climer

et al. 2014

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“…Despite progress in characterizing the structures of individual COG/Dsl1p/exocyst subunits, relatively little is known about how the subunits within each complex interact with one another (32,(34)(35)(36). One exception is the Dsl1p and Tip20p subunits of the Dsl1p complex, which were recently shown to interact via N-terminal ␣-helices (20).…”

Section: Discussionmentioning

confidence: 99%

Structural basis for a human glycosylation disorder caused by mutation of the COG4 gene

Richardson

Smith

Ungár

et al. 2009

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The proper glycosylation of proteins trafficking through the Golgi apparatus depends upon the conserved oligomeric Golgi (COG) complex. Defects in COG can cause fatal congenital disorders of glycosylation (CDGs) in humans. The recent discovery of a form of CDG, caused in part by a COG4 missense mutation changing Arg 729 to Trp, prompted us to determine the 1.9 Å crystal structure of a Cog4 C-terminal fragment. Arg 729 is found to occupy a key position at the center of a salt bridge network, thereby stabilizing Cog4's small C-terminal domain. Studies in HeLa cells reveal that this C-terminal domain, while not needed for the incorporation of Cog4 into COG complexes, is essential for the proper glycosylation of cell surface proteins. We also find that Cog4 bears a strong structural resemblance to exocyst and Dsl1p complex subunits. These complexes and others have been proposed to function by mediating the initial tethering between transport vesicles and their membrane targets; the emerging structural similarities provide strong evidence of a common evolutionary origin and may reflect shared mechanisms of action.congenital disorder of glycosylation ͉ Golgi apparatus ͉ multi-subunit tethering complex ͉ vesicle trafficking ͉ X-ray crystallography M ultiple lines of evidence implicate the conserved oligomeric Golgi (COG) complex in retrograde transport within the Golgi apparatus (1, 2). For example, partial knockdown of mammalian COG3 permitted exocytosis, while simultaneously blocking the retrograde transport of Shiga toxin from endosomes to the ER (3). COG was initially isolated from bovine brain on the basis of its ability to stimulate an in vitro Golgi transport assay (4). Two of its 8 subunits, Cog1/ldlB and Cog2/ ldlC, had previously been identified in a genetic screen for compromised cell surface receptor stability (5, 6). In the yeast Saccharomyces cerevisiae, the COG complex was discovered through studies of one of its subunits, Cog8p/Dor1p. Implicated in vesicle targeting to the Golgi apparatus, Cog8p was found to co-immunoprecipitate with 7 other polypeptides (7). The 7 associated polypeptides included two (Cog2p/Sec35p and Cog3p/ Sec34p) that had earlier been identified in genetic screens for temperature-sensitive mutations causing secretion defects (8). In further support of a role in trafficking to and within the Golgi, COG interacts physically with a large number of Golgi-localized trafficking factors, including (in yeast) the Rab family G protein Ypt1p, the SNAREs Sed5p, Ykt6p, Gos1p, and Sec22p, and COPI vesicle coat proteins (9).COG is one of several large protein complexes proposed to function as multisubunit tethering factors, mediating the initial interaction between transport vesicles and their target membranes (2, 10-12). For many of these complexes, a dearth of structural information has slowed the development of mechanistic models and has made it difficult to know how-or whether-to apply lessons learned from studies of one complex to another. Subunits of the COG, exocyst, Dsl1p, and Golgiassoci...

“…In mammalian cells, the virtually complete Cog1 deficiency affects the stability of all lobe B subunits while not dramatically affecting Cog2, -3, and -4 levels (7,9,13). In yeast, the interaction of the Cog2-4 subunits with the Cog5-8 subunits is disrupted in either Cog1-deficient cells or cells expressing Cog1 with an 80-residue truncation at the N terminus (33). We found that the truncated C terminus of Cog1 in our patient's cells was associated with an instability in Cog2-4 and Cog8, but not the Cog5-7 subcomplex.…”

Section: Effects Of Truncated Cog1 On Golgi Matrix Proteins and Enzymesmentioning

confidence: 99%

“…This relationship may be due to the possible role of COG in controlling intraGolgi trafficking of some resident Golgi proteins (e.g., COPI-dependent retrograde trafficking) (32). The analysis of human COG subunit mutations from CDG patients, together with mammalian somatic cell mutants, yeast mutants, and RNA interference knockdown studies (9,12,33), should help define the precise mechanism by which COG controls the structure and function of the Golgi apparatus.…”

Section: Effects Of Truncated Cog1 On Golgi Matrix Proteins and Enzymesmentioning

confidence: 99%

Conserved oligomeric Golgi complex subunit 1 deficiency reveals a previously uncharacterized congenital disorder of glycosylation type II

Foulquier¹,

Vasile²,

Schollen³

et al. 2006

164

149