Cloning and recombinant expression of a structurally novel human secreted phospholipase A(2)

Mammals contain a diverse set of secreted phospholipases A(2) (sPLA(2)s) th at liberate arachidonic acid from phospholipids for the production of eicos anoids and exert a variety of physiological and pathological effects. We re port the cloning, recombinant expression, and kinetic properties of a novel human sPLA(2) that defines a new structural class of sPLA(2)s called group XII. The human group XII (hGXII) cDNA contains a putative signal peptide o f 22 residues followed by a mature protein of 167 amino acids that displays homology to all known sPLA(2)s only over a short stretch of amino acids in the active site region. Northern blot and reverse transcription-polymerase chain reaction analyses show that the tissue distribution of hGXII is dist inct from the other human sPLA(2)s with strong expression in heart, skeleta l muscle, kidney, and pancreas and weaker expression in brain, liver, small intestine, lung, placenta, ovaries, testis, and prostate. Catalytically ac tive hGXII was produced in Escherichia coli and shown to be Ca2+-dependent despite the fact that it is predicted to have an unusual Ca2+-binding loop. Similar to the previously characterized mouse group IIE sPLA(2)s, the spec ific activity of hGXII is low in comparison to that of other mammalian sPLA (2), suggesting that hGXII could have novel functions that are independent of its phospholipase A(2) activity.