Direct interaction between the COG complex and the SM protein,Sly1, is required for Golgi SNARE pairing

The crucial roles of Sec1/Munc18 (SM)‐like proteins in membrane fusion have been evidenced in genetic and biochemical studies. SM proteins interact directly with SNAREs and contribute to SNARE pairing by a yet unclear mechanism. Here, we show that the SM protein, Sly1, interacts directly with the conserved oligomeric Golgi (COG) tethering complex. The Sly1–COG interaction is mediated by the Cog4 subunit, which also interacts with Syntaxin 5 through a different binding site. We provide evidence that disruption of Cog4–Sly1 interaction impairs pairing of SNAREs involved in intra‐Golgi transport thereby markedly attenuating Golgi‐to‐ER retrograde transport. These results highlight the mechanism by which SM proteins link tethering to SNAREpin assembly.