Structural implication for receptor oligomerization from functional reconstitution studies of mutant V2 vasopressin receptors

Previous studies have established that G-protein-coupled receptors (GPCRs) are composed of independent folding domains. Based on this findings we atte mpted to rescue the function of clinically relevant missense mutations (R13 7H, S167L, and R181C) within the N-terminal domain of the V2 vasopressin re ceptor (V2-R), by coexpressing mutated full-length (Y280C) and C-terminally truncated (E242X) receptor constructs in COS-7 cells. Coimmunoprecipitatio n and enzyme-linked immunosorbent assay studies demonstrated a specific ass ociation of E242X with full-length V2 Rs even in the presence of missense m utations. Systematic analysis of the structural requirements for the observ ed receptor/fragment association showed that N-terminal fragments containin g at least transmembrane regions 1-3 interact with the full-length V2-R. De spite this specific interaction, no functional reconstitution was achieved for mutant V2-Rs following coexpression with E242X and Y280C, However, func tional activity of R137H and R181C upon coexpression with E242X was regaine d by mutational disruption of the extracellular disulfide bond, which is hi ghly conserved among GPCRs. OUT data with the V2-R are consistent with a st ructural model in which class I GPCRs form contact oligomers by lateral int eraction rather than by a domain-swapping mechanism.