title: Novel mammalian group XII secreted phospholipase A2 lacking enzymatic activity.
abstract: An increasing number of mammalian secreted phospholipases A(2) (sPLA(2)s) has been identified over the past few years. Here, we report the identification and recombinant expression of a novel sPLA(2)-like protein in mouse and human species that has been called group XIIB (GXIIB). The mature protein has a molecular mass of 19.7 kDa and structural features similar to those of the previously identified GXII sPLA(2), now called GXIIA. Strikingly, the GXIIB sPLA(2) has a mutation in the active site, replacing the canonical histidine by a leucine, suggesting that this sPLA(2) is catalytically inactive. Recombinant expression of human (hGXIIB) and mouse (mGXIIB) sPLA(2)s in Escherichia coli indicates that GXIIB sPLA(2)s display no measurable lipolytic activity on various types of phospholipid substrates. Furthermore, these sPLA(2)-like proteins display relatively weak affinity to phospholipid vesicles. Binding experiments indicate that these proteins are also unable to bind to the well-known M-type sPLA(2) receptor. The RNA tissue distribution of GXIIB sPLA(2)s is distinct from that of other sPLA(2)s including the homologous GXIIA. Strong expression was observed in liver, small intestine, and kidney in both human and mouse species. Interestingly, the expression of the novel sPLA(2) is dramatically decreased in human tumors from the same tissues. The absence of enzymatic activity suggests that the GXIIB sPLA(2)-like proteins probably exert their biological roles by acting as ligands for as yet unidentified receptors.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010741:Phospholipases A / Q000235:genetics* / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D054507:Receptors, Phospholipase A2; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
chemical_list: C516360:PLA2R1 protein, human; D010743:Phospholipids; C516357:Pla2r1 protein, mouse; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054507:Receptors, Phospholipase A2; D011994:Recombinant Proteins; D010741:Phospholipases A; D054467:Phospholipases A2