Serine phospholipid-specific phospholipase A that is secreted from activated platelets. A new member of the lipase family.
Rat platelets secrete two types of phospholipases upon stimulation; one is type II phospholipase A2 and the other is serine-phospholipid-selective phospholipase A. In the current study we purified serine-phospholipid-selective phospholipase A and cloned its cDNA. The final preparation, purified from extracellular medium of activated rat platelets, gave a 55-kDa protein band on SDS-polyacrylamide gel electrophoresis. [3H]Diisopropyl fluorophosphate, an inhibitor of the enzyme, labeled the 55-kDa protein, suggesting that this polypeptide possesses active serine residues. The cDNA for the enzyme was cloned from a rat megakaryocyte cDNA library. The predicted 456-amino acid sequence contains a putative short N-terminal signal sequence and a GXSXG sequence, which is a motif of an active serine residue of serine esterase. Amino acid sequence homology analysis revealed that the enzyme shares about 30% homology with mammalian lipases (lipoprotein lipase, hepatic lipase, and pancreatic lipase). Regions surrounding the putative active serine, histidine, and aspartic acid, which may form a "lipase triad," were highly conserved among these enzymes. The recombinant protein, which we expressed in Sf9 insect cells using the baculovirus system, hydrolyzed a fatty acyl residue at the sn-1 position of lysophosphatidylserine and phosphatidylserine, but did not appreciably hydrolyze phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidic acid, and triglyceride. The present enzyme, named phosphatidylserine-phospholipase A1, is the first phospholipase that exclusively hydrolyses the sn-1 position and has a strict head group specificity for the substrate.
Sato
T
T
Faculty of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan.
Aoki
J
J
Nagai
Y
Y
Dohmae
N
N
Takio
K
K
Doi
T
T
Arai
H
H
Inoue
K
K
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000201:enzymology*; D018076:DNA, Complementary / Q000737:chemistry; D007531:Isoflurophate / Q000378:metabolism; D008245:Lysophospholipase / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010741:Phospholipases A / Q000737:chemistry* / Q000378:metabolism; D054467:Phospholipases A2; D015539:Platelet Activation; D011480:Protease Inhibitors / Q000378:metabolism; D051381:Rats; D016415:Sequence Alignment; D013917:Thrombin / Q000494:pharmacology
D018076:DNA, Complementary; D011480:Protease Inhibitors; D007531:Isoflurophate; D010741:Phospholipases A; D054467:Phospholipases A2; D008245:Lysophospholipase; D013917:Thrombin