Molecular characterization of murine pancreatic phospholipase A(2)

Structural characteristics and evolution of the Protobothrops elegans pancreatic phospholipase A2 gene in contrast with those of Protobothrops genus venom phospholipase A2 genes

The nucleotide sequence of the gene encoding Protobothrops elegans (Crotalinae) pancreatic phospholipase A(2) (PLA(2)), abbreviated PePancPLA(2), was determined by means of inverted PCR techniques. Since its deduced amino acid sequence contains a pancreatic loop and shows high similarity to that of Laticauda semifasciata (Elapinae) group IB pancreatic PLA(2), PePancPLA(2) is classified into group IB PLA(2). The nucleotide sequences of the PePancPLA(2) gene, the L. semifasciata group IB pancreatic PLA(2) gene, and the L. semifasciata group IA venom PLA(2) gene are similar to one another but greatly dissimilar to those of Protobothrops genus (Crotalinae) group II venom PLA(2) genes, suggesting that the Elapinae group IB PLA(2) gene and the group IA PLA(2) gene appeared after Elapinae was established, and that the Crotalinae group II venom PLA(2) genes came into existence before Elapinae and Crotalinae diverged. A phylogenetic analysis of their amino acid sequences confirms this.

Purification and biochemical characterization of pancreatic phospholipase A2 from the common stingray Dasyatis pastinaca

BACKGROUND

Mammalian sPLA2-IB are well characterized. In contrast, much less is known about aquatic ones. The aquatic world contains a wide variety of living species and, hence represents a great potential for discovering new lipolytic enzymes.

RESULTS

A marine stingray phospholipase A2 (SPLA2) was purified from delipidated pancreas. Purified SPLA2, which is not glycosylated protein, was found to be monomeric protein with a molecular mass of 14 kDa. A specific activity of 750 U/mg for purified SPLA2 was measured at optimal conditions (pH 8.5 and 40 °C) in the presence of 4 mM NaTDC and 8 mM CaCl2 using PC as substrate. The sequence of the first twenty first amino-acid residues at the N-terminal extremity of SPLA2 was determined and shows a close similarity with known mammal and bird pancreatic secreted phospholipases A2. SPLA2 stability in the presence of organic solvents, as well as in acidic and alkaline pH and at high temperature makes it a good candidate for its application in food industry.

CONCLUSIONS

SPLA2 has several advantageous features for industrial applications. Stability of SPLA2 in the presence of organic solvents, and its tolerance to high temperatures, basic and acidic pH, makes it a good candidate for application in food industry to treat phospholipid-rich industrial effluents, or to synthesize useful chemical compounds.

Emerging roles of secreted phospholipase A2 enzymes: Lessons from transgenic and knockout mice

Among the emerging phospholipase A(2) (PLA(2)) superfamily, the secreted PLA(2) (sPLA(2)) family consists of low-molecular-mass, Ca(2+)-requiring extracellular enzymes with a His-Asp catalytic dyad. To date, more than 10 sPLA(2) enzymes have been identified in mammals. Individual sPLA(2)s exhibit unique tissue and cellular localizations and enzymatic properties, suggesting their distinct pathophysiological roles. Despite numerous enzymatic and cell biological studies on this enzyme family in the past two decades, their precise in vivo functions still remain largely obscure. Recent studies using transgenic and knockout mice for several sPLA(2) enzymes, in combination with lipidomics approaches, have opened new insights into their distinct contributions to various biological events such as food digestion, host defense, inflammation, asthma and atherosclerosis. In this article, we overview the latest understanding of the pathophysiological functions of individual sPLA(2) isoforms fueled by studies employing transgenic and knockout mice for several sPLA(2)s.

Neutral ceramidase gene: role in regulating ceramide-induced apoptosis

The sphingolipid, ceramide, is a natural dietary constituent and a potent mediator of apoptosis. If left undegraded, it may induce apoptosis and cause disruption of cellular integrity. A potential mechanism to prevent ceramide-induced apoptosis in various organs may involve ceramidases that facilitate the degradation of ceramide. In this study, we first isolated and characterized the murine neutral ceramidase (N-CDase) gene, mapped its chromosomal location and determined its developmental and organ-specific expression. Then we used cultured mesangial cells as our in vitro model and mouse gastrointestinal (GI) tract as the in vivo model to determine the effects of an inhibitor of N-CDase, D-erythro-MAPP, to delineate whether N-CDase plays a role in preventing ceramide-induced apoptosis. Our results show that: (i) the structure of the murine neutral ceramidase gene is virtually identical to that of the human gene; (ii) it is localized on chromosome 19 at bands C2-C3 that is syntenic to human chromosome 10q24-26; (iii) N-CDase expression is developmentally regulated and it is expressed at high levels in cultured mesangial cells and in specific regions of the mouse small intestine; (iv) inhibition of N-CDase by D-erythro-MAPP leads to increased ceramide levels and consequent apoptosis in cultured mesangial cells; (v) mice treated with D-erythro-MAPP alone also caused apoptosis in the small intestine; and (vi) mice treated with D-erythro-MAPP prior to feeding C2 ceramide manifest markedly elevated levels of apoptosis in the GI tract raising the possibility that neutral ceramidase plays a detoxifying role against inadvertent stimulation of ceramide-induced apoptosis in organs that come in contact with this sphingolipid. We propose that N-CDase is an essential component of an innate detoxifying mechanism to prevent ceramide-induced apoptosis.

Lys 43 and Asp 46 in alpha-helix 3 of uteroglobin are essential for its phospholipase A2 inhibitory activity

Uteroglobin (UG) is an anti-inflammatory, secreted protein with soluble phospholipase A2 (sPLA2)-inhibitory activity. However, the mechanism by which UG inhibits sPLA2 activity is unknown. UG is a homodimer in which each of the 70-amino acid subunits forms four alpha-helices. We previously reported that sPLA2-inhibitory activity of UG may reside in a segment of alpha-helix 3 that is exposed to the solvent. In addition, it has been suggested that UG may inhibit sPLA2 activity by binding and sequestering Ca++, essential for sPLA2 activation. By site-specific mutation, we demonstrate here that Lys 43 Glu, Asp 46 Lys or a combination of the two mutations in the full-length, recombinant human UG (rhUG) abrogates its sPLA2-inhibitory activity. We demonstrate further that recombinant UG does not bind Ca++ although when it is expressed with histidine-tag (H-tag) it is capable of binding Ca++. Taken together our results show that: (i) Lys 43 and Asp 46 in rhUG are critical residues for the sPLA2-inhibitory activity of UG and (ii) Ca++-sequestration by rhUG is not likely to be one of the mechanisms responsible for its sPLA2-inhibitory activity.