SYNTHESIS AND PROCESSING OF D2-DOPAMINE RECEPTORS

Dopamine receptors belong to a superfamily of neurotransmitter recepto rs that are functionally coupled to guanine nucleotide binding protein s. In this study, we have used Chinese hamster ovary (CHO) cells stabl y transfected with the rat D2L receptor, in conjunction with specific anti-peptide antibodies that we have developed, in order to visualize this protein and the course of its synthesis. The newly synthesized re ceptor exists as a 45-kDa protein which undergoes further processing t o a 75-kDa glycosylated receptor in the CHO cells. In pulse-chase expe riments it was noticed that a 35-kDa precursor was present which disap peared after 30 min. In order to determine whether this 35-kDa protein represents an unprocessed form of the receptor, we have employed an i n vitro translation system with cDNA constructs coding for both the mu rine D2 and D3 dopamine receptor isoforms. In the absence of processin g, the D2 and D3 receptors have an apparent molecular mass of 35 kDa. The translated proteins were shown to be the full length receptors by immunoprecipitation with various anti-peptide antibodies and by the de monstration that they can undergo glycosylation to apparent molecular masses of approximately 45 kDa in an in vitro system.