Coat-tether interaction in Golgi organization

Biogenesis of the Golgi apparatus is likely mediated by the COPI vesicle coat complex, but the mechanism is poorly understood. Modeling of the COPI subunit beta COP based on the clathrin adaptor AP2 suggested that the beta COP C terminus forms an appendage domain with a conserved FW binding pocket motif. On gene replacement after knockdown, versions of beta COP with a mutated FW motif or flanking basic residues yielded a defect in Golgi organization reminiscent of that occurring in the absence of the vesicle tether p115. Indeed, beta COP bound p115, and this depended on the beta COP FW motif. Furthermore, the interaction depended on E19E21 in the p115 head domain and inverse charge substitution blocked Golgi biogenesis in intact cells. Finally, Golgi assembly in permeabilized cells was significantly reduced by inhibitors containing intact, but not mutated, beta COP FW or p115 EE motifs. Thus, Golgi organization depends on mutually interacting domains in beta COP and p115, suggesting that vesicle tethering at the Golgi involves p115 binding to the COPI coat.