Novel human secreted phospholipase A(2) with homology to the group III beevenom enzyme

Venom and mammalian secreted phospholipases A, (sPLA(2)s) have been associa ted with numerous physiological, pathological, and toxic processes. So far, structurally related group I and II sPLA(2)s have been found in vertebrate s such as mammals and snakes, whereas group In: sPLA(2)s have mainly been f ound in venom from invertebrates such as bees and scorpions Here we report the cloning and expression of a cDNA coding for a human group III (hGIII) s PLA(2). The full-length cDNA codes for a signal peptide of 19 residues foll owed by a protein of 490 amino acids made up of a central sPLA(2), domain ( 141 residues) flanked by large N- and C-terminal regions (130 and 219 resid ues, respectively). The sPLA(2) domain is 31% identical to bee venom sPLA(2 ) and displays all of the features of group III sPLA(2)s including 10 cyste ines. The hGIII sPLA(2) gene consists of at least 7 exons and maps to chrom osome 22q. By Northern blot analysis, a 4.4-kilobase hGIII transcript was f ound in kidney, heart, liver, and skeletal muscle. Transfection of hGIII sP LA(2) cDNA in COS cells led to accumulation of sPLA(2) activity in the cult ure medium, indicating that the cDNA codes for a secreted enzyme, Using sma ll unilamellar vesicles as substrate, hGIII sPLA(2) was found to be a Ca2+- dependent enzyme showing an 11-fold preference for phosphatidylglycerol ove r phosphatidylcholine and optimal activity at pH 8.