Coimmunoprecipitation of the mutant CaR, R795W, with the truncated CaR, A877Stop (A), and an inactive truncated CaR (A877Stop or R795W&A877Stop) with the inactive full-length mutant CaR, G143E (B). HEK cells transfected or cotransfected with Flag-tagged and nontagged CaRs (as indicated in the figure) were biotinylated before cell lysis in the presence of 100 mM iodoacetamide. After immunoprecipitation with anti-Flag antibody, elution with SDS sample buffer with DTT, and SDS/PAGE (3–10%), CaR surface expression was detected with avidin.