Cloning and recombinant expression of a novel mouse-secreted phospholipaseA(2)

Secreted phospholipases A(2) (sPLA(2)s) form a class of structurally relate d enzymes that are involved in a variety of physiological and pathological effects including inflammation and associated diseases, cell proliferation, cell adhesion, and cancer, and are now known to bind to specific membrane receptors. Here, we report the cloning and expression of a novel sPLA(2) is olated from mouse thymus, Based on its structural features, this sPLA(2) is most similar to the previously cloned mouse group ILA sPLA(2) (mGIIA sPLA( 2)). As for mGIIA sPLA(2), the novel sPLA(2) is made up of 125 amino acids with 14 cysteines, is basic (pI = 8.71) and its gene has been mapped to mou se chromosome 4, However, the novel sPLA(2) has only 48% identity with mGII A and displays similar levels of identity with the other mouse group IIC an d V sPLA(2)s, indicating that the novel sPLA(2) is not an isoform of mGIIA sPLA(2). This novel sPLA(2) has thus been called mouse group IID (mGIID) sP LA(2). In further contrast with mGIIA, which is found mainly in intestine, transcripts coding for mGIID sPLA(2) are found in several tissues including pancreas, spleen, thymus, skin, lung, and ovary, suggesting distinct funct ions for the two enzymes. Recombinant expression of mGIID sPLA(2) in Escher ichia coli indicates that the cloned sPLA(2) is an active enzyme that has m uch lower specific activity than mGIIA and displays a distinct specificity for binding to various phospholipid vesicles. Finally, recombinant mGIID sP LA(2) did not bind to the mouse M-type sPLA(2) receptor, while mGIIA was pr eviously found to bind to this receptor with high affinity.