The Conserved Oligomeric Golgi (COG) complex is a hetero-octameric peripheral Golgi protein complex that is believed to play a role in maintaining the structure and function of the Golgi apparatus. It appears to be involved in intra-Golgi vesicle-mediated transport, endoplasmic reticulum to Golgi vesicle-mediated anterograde transport and the regulation of endosome to trans-Golgi network (TGN) retrograde trafficking. It is also involved in glycosylation through the trafficking of glycosyltransferases.
While the exact mechanism by which the COG complex mediates its functions is unclear, recent studies have highlighted the role of a subunit named COG6. This subunit, located in lobe B of the complex, is encoded by the COG6 gene and allows the complex to interact directly with target membrane SNARE Syntaxin 6. Depletion of mouse Cog6 in cells leads to a reduction in the steady-state level of Syntaxin 6 and significantly diminishes endosome to TGN transport.
Defects in the COG6 gene can thus have strong pathological consequences. Homozygous COG6 mutations have been implicated in Congenital Disorder of Glycosylation, type IIl (CDG2L) and Shaheen Syndrome.