Molecular cloning of two new human paralogs of 85-kDa cytosolic phospholipase A2

Two new cloned human cDNAs encode paralogs of the 85-kDa cytosolic phospholipase A(2) (cPLA(2)). We propose to call these cPLA(2)beta (114 kDa) and cPLA(2)gamma (61 kDa), giving the name cPLA(2)alpha to the well known 85-kDa enzyme. cPLA(2)beta mRNA is expressed more highly in cerebellum and pancreas and cPLA(2)gamma more highly in cardiac and skeletal muscle, Sequence-tagged site mapping places cPLA(2)beta on chromosome 15 in a region near a phosphoinositol bisphosphate phosphatase. The mRNA for cPLA(2)beta is spliced only at a very low level, and Northern blots in 24 tissues show exclusively the unspliced form. cPLA(2)beta has much lower activity on 2-arachidonoyl-phosphatidylcholine liposomes than either of the other two enzymes. Its sequence contains a histidine motif characteristic of the catalytic center of caspase proteases of the apoptotic cascade but no region characteristic of the catalytic cysteine, Sequence-tagged site mapping places cPLA(2)gamma on chromosome 19 near calmodulin, cPLA(2)gamma lacks the C2 domain, which gives cPLA(2)alpha its Ca(2+) sensitivity, and accordingly cPLA(2)gamma has no dependence upon calcium, although cPLA(2)beta does, cPLA(2)gamma contains a prenyl group-binding site motif and appears to be largely membrane-bound. cPLA(2)alpha residues activated by phosphorylation do not appear to be well conserved in either new enzyme. In contrast, all three previously known catalytic residues, as well as one additional essential arginine, Arg-566 in cPLA(2)alpha, are conserved in both new enzyme sequences. Mutagenesis shows strong dependence on these residues for catalytic activity of all three enzymes.