A yeast Golgi E-type ATPase with an unusual membrane topology.
E-type ATPases are involved in many biological processes such as modulation of neural cell activity, prevention of intravascular thrombosis, and protein glycosylation. In this study, we show that a gene of Saccharomyces cerevisiae, identified by similarity to that of animal ectoapyrase CD39, codes for a new member of the E-type ATPase family (Apy1p). Overexpression of Apy1p in yeast cells causes an increase in intracellular membrane-bound nucleoside di- and triphosphate hydrolase activity. The activity is highest with ADP as substrate and is stimulated similarly by Ca (2+), Mg(2+), and Mn(2+). The results also indicate that Apy1p is an integral membrane protein located predominantly in the Golgi compartment. Sequence analysis reveals that Apy1p contains one large NH(2)-terminal hydrophilic apyrase domain, one COOH-terminal hydrophilic domain, and two hydrophobic stretches in the central region of the polypeptide. Although no signal sequence is found at the NH(2)-terminal portion of the protein and no NH(2)-terminal cleavage of the protein is observed, demonstrated by the detection of NH(2)-terminal tagged Apy1p, the NH(2)-terminal domain of Apylp is on the luminal side of the Golgi apparatus, and the COOH-terminal hydrophilic domain binds to the cytoplasmic face of the Golgi membrane. The second hydrophobic stretch of Apy1p is the transmembrane domain. These results indicate that Apylp is a type III transmembrane protein; however, the size of the Apy1p extracytoplasmic NH(2) terminus is much larger than those of other type III transmembrane proteins, suggesting that a novel translocation mechanism is utilized.
Zhong
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Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Guidotti
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D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics*; D000408:Alamethicin / Q000494:pharmacology; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry; D001081:Apyrase; D001483:Base Sequence; D002413:Cations, Divalent / Q000494:pharmacology; D003001:Cloning, Molecular; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry / Q000235:genetics*; D003902:Detergents / Q000494:pharmacology; D019286:Endopeptidase K; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics; D005800:Genes, Fungal; D006056:Golgi Apparatus / Q000201:enzymology*; D007425:Intracellular Membranes / Q000201:enzymology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009708:Nucleotidases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
D015703:Antigens, CD; C088829:ApY1 protein, Aplysia californica; D002413:Cations, Divalent; D017362:Cyclic AMP Response Element-Binding Protein; D003902:Detergents; D005656:Fungal Proteins; D008565:Membrane Proteins; D000408:Alamethicin; D009708:Nucleotidases; D019286:Endopeptidase K; D000251:Adenosine Triphosphatases; D001081:Apyrase; C067869:CD39 antigen