Purification and characterization of a major phosphatidylserine-binding phosphoprotein from human platelets.
We describe the isolation, lipid-binding properties and partial amino acid sequence of PS-p68, a novel 68 kDa phosphatidylserine-binding protein from human platelets. PS-p68 is an abundant constituent of platelets, accounting for 0.5-0.75% of total cell protein. It was purified from platelet cytosol by affinity chromatography. Amino acid sequence analysis yielded no similarity to identified proteins. In contrast with most known phospholipid-binding proteins, PS-p68 does not bind Ca2+ and does not require Ca2+ for its binding of phosphatidylserine. Phosphatidylserine binding to PS-p68 was inhibited by phosphatidic acid and by alkylphospholipids. PS-p68 was isolated as a major phosphoprotein from 32P-labelled platelets and was found to function as a protein kinase C substrate in vitro. However, treatment of intact platelets with phorbol 12-myristate 13-acetate, thrombin or carbacyclin did not increase PS-p68 phosphorylation. Platelets appear to be the only blood cells containing PS-p68, which was not detected in neutrophils, monocytes and lymphocytes.
Burgener
R
R
Theodor Kocher Institut, Universität Bern, Switzerland.
Wolf
M
M
Ganz
T
T
Baggiolini
M
M
D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000032:analysis* / Q000648:ultrastructure; D001798:Blood Proteins / Q000302:isolation & purification* / Q000378:metabolism; D002352:Carrier Proteins / Q000097:blood* / Q000302:isolation & purification / Q000378:metabolism; D003101:Collodion / Q000378:metabolism; D003600:Cytosol / Q000032:analysis; D006801:Humans; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D014018:Tissue Distribution
D001798:Blood Proteins; D002352:Carrier Proteins; D010750:Phosphoproteins; D003101:Collodion