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35
The role of COG subcomplexes in the intra-Golgi
vesicular trafficking
Vladimir Lupashin 1 , Irina Pokrovskaya 1 , Rose Willett 1 , Richard Smith 1 .
University of Arkansas for Medical Sciences, Department of Physiology and Biophysics 1
Abstract:
The Conserved Oligomeric Golgi (COG) complex is a ubiquitously expressed membraneassociated
protein complex that consists of eight different subunits (Cog1-8). COG functions in
the retrograde intra-Golgi trafficking through association with coiled-coil tethers, SNAREs,
Rabs and COPI proteins. Yeast genetic studies indicated that the COG complex consists of two
functional subcomplexes: LobeA (Cog1-4) and LobeB (Cog5-8), but the exact relationship
between these subcomplexes was not known. Quantitative IP experiments and gel-filtration
analysis demonstrated that the cytoplasmic COG complex is a stable octamer, while half of the
membrane-bound COG complex partitions into at least two sub-complexes. Depletion of the
Golgi SNARE Syntaxin5 augments partitioning of the COG complex into the sub-complexes,
indicating that Syntaxin5 positively regulates intra-COG complex assembly. Live cell microscopy
of HeLa cells stably expressing CFP-Cog6/YFP-Cog3 reveals that Cog6 (Lobe B) is associated
with both the Golgi membrane, and small vesicles carrying Golgi enzyme GlcNAcT1. GlcNAcT1
vesicles were also positive for Cog8, and likely correspond to the intra-Golgi trafficking
intermediates. In contrast, Cog3(LobeA) was not found on vesicles and was exclusively
associated with Golgi membranes. This hints that the transient assembly of COG sub-complexes
is the initial step in intra-Golgi vesicle tethering. Relocalization of the siRNA resistant COG
complex subunits to the mitochondria, using either mitochondria-specific membrane anchor or
a “knocksideways” strategy, was employed to divert COG-specific vesicular trafficking from the
secretory pathway and elucidate additional specific features of the COG subcomplexes.
Supported by grants MCB0645163 and GM083144