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 reading frame encoding a hydrophobic polypeptide of 514 amino acids with twelve membrane spanning segments, a calculated molecular weight of 55,709 Da, and an estimated isoelectrical point of 5.62. A structurally identical transporter is expressed in human platelets. Two intraplasmatic consensus phosphorylation sites of cAMP-dependent protein kinase recognition and two potential protein kinase C phosphorylation sites may be central to the regulation of the VMT. Although the human brain VMT is 90.7% homologous to the rat protein, an extensive sequence divergence occurs in the large luminal loop located between the first two transmembrane domains. This loop displays a remarkably reduced homology of 64.0% with several deletions and insertions, although four putative glycosylation sites are conserved. Since functional vesicular monoamine transport suppresses MPP+ toxicity and sequence divergence in the large luminal loop of the VMT expressed in rat brain and adrenal medulla may play a role in differential neurotoxic effects of MPP+, our findings indicate one possible molecular basis for the substantial species differences in the susceptibility to MPP+ demonstrated among humans, non-human primates, and rodents. They are also likely to facilitate molecular pharmacologic and genetic investigations of the human VMT in neurodegenerative disorders.
Lesch
K P
KP
Department of Psychiatry, University of Würzburg, Federal Republic of Germany.
Gross
J
J
Wolozin
B L
BL
Murphy
D L
DL
Riederer
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004351:Drug Resistance; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009479:Neuropeptides; D015345:Oligonucleotide Probes / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods; D011726:Pyridinium Compounds / Q000494:pharmacology*; D051381:Rats / Q000235:genetics*; D017385:Sequence Homology; D013045:Species Specificity; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
D006023:Glycoproteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D015345:Oligonucleotide Probes; D011726:Pyridinium Compounds; C493452:SLC18A2 protein, human; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; C026560:1-(4-methoxyphenyl)pyridinium; D004247:DNA