EXTENSIVE SEQUENCE DIVERGENCE BETWEEN THE HUMAN AND RAT-BRAIN VESICULAR MONOAMINE TRANSPORTER - POSSIBLE MOLECULAR-BASIS FOR SPECIES-DIFFERENCES IN THE SUSCEPTIBILITY TO MPP+

A cDNA encoding the human brain vesicular monoamine transporter (VMT) was isolated and sequenced using PCR. The cDNA contains an open readin g frame encoding a hydrophobic polypeptide of 514 amino acids with twe lve membrane spanning segments, a calculated molecular weight of 55,70 9 Da, and an estimated isoelectrical point of 5.62. A structurally ide ntical transporter is expressed in human platelets. Two intraplasmatic consensus phosphorylation sites of cAMP-dependent protein kinase reco gnition and two potential protein kinase C phosphorylation sites may b e central to the regulation of the VMT. Although the human brain VMT i s 90.7% homologous to the rat protein, an extensive sequence divergenc e occurs in the large luminal loop located between the first two trans membrane domains. This loop displays a remarkably reduced homology of 64.0% with several deletions and insertions, although four putative gl ycosylation sites are conserved. Since functional vesicular monoamine transport supresses MPP+ toxicity and sequence divergence in the large luminal loop of the VMT expressed in rat brain and adrenal medulla ma y play a role in differential neurotoxic effects of MPP+, our findings indicate one possible molecular basis for the substantial species dif ferences in the suceptibility to MPP+ demonstrated among humans, non-h uman primates, and rodents. They are also likely to facilitate molecul ar pharmacologic and genetic investigations of the human VMT in neurod egenerative disorders.