Cloning and recombinant expression of a novel mouse-secreted phospholipase A2

Secreted phospholipases A(2) (sPLA(2)s) form a class of structurally related 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) isolated 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 mouse chromosome 4, However, the novel sPLA(2) has only 48% identity with mGIIA and displays similar levels of identity with the other mouse group IIC and 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) sPLA(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 functions for the two enzymes. Recombinant expression of mGIID sPLA(2) in Escherichia coli indicates that the cloned sPLA(2) is an active enzyme that has much lower specific activity than mGIIA and displays a distinct specificity for binding to various phospholipid vesicles. Finally, recombinant mGIID sPLA(2) did not bind to the mouse M-type sPLA(2) receptor, while mGIIA was previously found to bind to this receptor with high affinity.