Figure 5: Hypothetical model of lobe A-lobe B interaction mediated vesicle tethering.

Hypothetical model of how lobe A and lobe B interaction mediates the tethering of an incoming retrograde vesicle. (A) Incoming vesicle containing a v-SNARE (example GS15) and lobe B sub-complex, will begin its tethering via interaction with a coiled-coil tether (example P115) from a further distance (A-I). Coiled-coil tether vesicle sequestration pulls the vesicle into close enough proximity to the Golgi membrane that lobe A and lobe B on opposing membranes will interact (A-II). Interaction between lobe A and lobe B (via COG1-COG8 direct protein-protein interaction) organizes the vesicle for proper alignment of the v-SNARE to the pre-assembled t-SNARE complex (example STX5/GS27/GS28/GS15 containing SNARE complex) (A-III). Aligned SNAREs then allow for vesicle docking and SNARE-pin formation to drive vesicle fusion (A-IV). If lobe A-lobe B interaction is required for COG mediated vesicle tethering, then defects in lobe A-lobe B interaction (B), or stabilization of octameric COG (C) would block the productive tether of incoming vesicle and prevent its fusion with the Golgi.