Structure of the cytoplasmic domain of p23 in solution: Implications for the formation of COPI vesicles

Coatomer, the coat protein complex of coat protein (COPI) vesicles, is invo lved in the budding of these vesicles. Its interaction with the cytoplasmic domains of some p24-family members, type I transmembrane proteins of the G olgi, has been shown to induce a conformational change of coatomer that ini tiates polymerization of the complex. From stoichiometrical data it is like ly that interaction of coatomer with the small tail domains involves an oli gomeric form of the p24 proteins. Here we present the structure of peptide analogs of the cytoplasmic domain of p23, a member of the p24 family, as de termined by two-dimensional nuclear magnetic resonance spectroscopy in the presence of 2,2,2-trifluoroethanol. An improved strategy for structure calc ulation revealed that the tail domain peptides form a-helices and adopt a t etrameric state. Based on these results we propose an initial model for the binding of coatomer by p23 and the induced conformational change of coatom er that results in its polymerization, curvature of the Golgi membrane to f orm a bud, and finally a COPI-coated vesicle. (C) 2000 Academic Press.