Identification and characterization of a soluble form of the plasma cell membrane glycoprotein PC-1 (5'-nucleotide phosphodiesterase).
PC-1 is a membrane glycoprotein, found on the surface of plasma cells and a few types of nonlymphoid cells, which has recently been found to have 5'-nucleotide phosphodiesterase activity. In this paper, we demonstrate the existence of enzymically active water-soluble forms of PC-1 in ascites from plasmacytoma-bearing mice, normal mouse serum, and in supernatants of cultured mouse plasmacytoma cells and mouse L cells transfected with a cDNA encoding the membrane form of PC-1. The water-soluble enzyme activity can be specifically immunoprecipitated by a monoclonal antibody to an allotypic determinant on the membrane form of PC-1, and resides on a slightly smaller polypeptide than membrane PC-1. Biosynthetic studies revealed a single, monomeric, endoglycosidase-H-sensitive membrane PC-1 precursor, which was gradually converted to a disulphide-bonded, endoglycosidase-H-resistant form over a period of about 2 h. Soluble PC-1 was first detectable in the supernatant after about 2 h. A distinct intracellular form of soluble PC-1 was not seen. The soluble form of PC-1 does not appear to arise by proteolytic cleavage from the cell surface, although cleavage inside the cell remains a possibility. When taken together with the structure of the relevant portions of PC-1 gene exons, the data suggest that the most likely site of cleavage is between Pro152 and Ala153.
Belli
S I
SI
Department of Pathology and Immunology, Monash Medical School, Victoria, Australia.
van Driel
I R
IR
Goding
J W
JW
D000595:Amino Acid Sequence; D000818:Animals; D001202:Ascitic Fluid / Q000737:chemistry; D001483:Base Sequence; D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology*; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons; D007163:Immunosorbent Techniques; D007739:L Cells; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010954:Plasmacytoma / Q000378:metabolism; D011755:Pyrophosphatases; D014162:Transfection; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D008562:Membrane Glycoproteins; D010727:Phosphoric Diester Hydrolases; D043264:Phosphodiesterase I; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases