Human secretory phospholipase A2, group IB in normal eyes and in eye diseases

High-affinity selective inhibitor against phospholipase A2 (PLA2): a computational study

Phospholipase A2 (PLA2) is the most abundant protein found in snake venom. PLA2 induces a variety of pharmacological effects such as neurotoxicity, myotoxicity and cardiotoxicity as well as anticoagulant, hemolytic, anti-platelet, hypertensive, hemorrhagic and edema inducing effects. In this study, the three dimensional structure of PLA2 of Naja sputatrix (Malayan spitting cobra) was modeled by I-TASSER, SWISS-MODEL, PRIME and MODELLER programs. The best model was selected based on overall stereo-chemical quality. Further, molecular dynamics simulation was performed to know the stability of the modeled protein using Gromacs software. Average structure was generated during the simulation period of 10 ns. High throughput virtual screening was employed through different databases (Asinex, Hit finder, Maybridge, TOSLab and ZINC databases) against PLA2. The top seven compounds were selected based on the docking score and free energy binding calculations. These compounds were analyzed by quantum polarized ligand docking, induced fit docking and density functional theory calculation. Furthermore, the stability of lead molecules in the active site of PLA2 was employed by MD simulation. The results show that selected lead molecules were highly stable in the active site of PLA2.

Maintenance of synaptic stability requires calcium-independent phospholipase A₂ activity

Phospholipases A₂ (PLA₂s) represent one of the largest groups of lipid-modifying enzymes. Over the years, significant advances have been made in understanding their potential physiological and pathological functions. Depending on their calcium requirement for activation, PLA₂s are classified into calcium dependent and independent. This paper mainly focuses on brain calcium-independent PLA₂ (iPLA₂) and on the mechanisms by which they influence neuronal function and regulate synaptic plasticity. Particular attention will be given to the iPLA₂γ isoform and its role in the regulation of synaptic glutamate receptors. In particular, the paper discusses the possibility that brain iPLA₂γ deficiencies could destabilise normal synaptic operation and might contribute to the aetiology of some brain disorders. In this line, the paper presents new data indicating that iPLA₂γ deficiencies accentuate AMPA receptor destabilization and tau phosphorylation, which suggests that this iPLA₂ isoform should be considered as a potential target for the treatment of Tau-related disorders.

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.

A phospholipase A₂ isolated from Lachesis muta snake venom increases the survival of retinal ganglion cells in vitro

We have previously showed that a phospholipase A₂ isolated from Lachesis muta snake venom and named LM-PLA₂-I displayed particular biological activities, as hemolysis, inhibition on platelet aggregation, edema induction and myotoxicity. In the present work, we evaluated the effect of LM-PLA₂-I on the survival of axotomized rat retinal ganglion cells kept in vitro, as well as its mechanism of action. Our results clearly showed that treatment with LM-PLA₂-I increased the survival of ganglion cells (100% when compared to control cultures) and the treatment of LM-PLA₂-I with p-bromophenacyl bromide abolished this effect. This result indicates that the effect of LM-PLA₂-I on ganglion cell survival is entirely dependent on its enzymatic activity and the generation of lysophosphatidylcholine (LPC) may be a prerequisite to the observed survival. In fact, commercial LPC mimicked the effect of LM-PLA₂-I upon ganglion cell survival. To investigate the mechanism of action of LM-PLA₂-I, cultures were treated with chelerythrine chloride, BAPTA-AM, rottlerin and also with an inhibitor of c-junc kinase (JNKi). Our results showed that rottlerin and JNK inhibitor abolished the LM-PLA₂-I on ganglion cell survival. Taken together, our results showed that LM-PLA₂-I and its enzymatic product, LPC promoted survival of retinal ganglion cells through the protein kinase C pathway and strongly suggest a possible role of the PLA₂ enzyme and LPC in controlling the survival of axotomized neuronal cells.

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.

Expression profile of multiple secretory phospholipase A(2) isoforms in the rat CNS: enriched expression of sPLA(2)-IIA in brainstem and spinal cord

Phospholipases A(2) (PLA(2)) are enzymes which cleave the sn-2 ester bond in membrane phospholipids to release free fatty acids and lysophospholipids. The present study aimed to elucidate the expression profile of multiple secretory phospholipase A(2) (sPLA(2)) isoforms in the normal rat CNS with focus on sPLA(2)-IIA in the brainstem and spinal cord. Quantitative RT-PCR analysis showed that sPLA(2)-IB expression was low throughout the CNS, sPLA(2)-IIA expression was high in the brainstem and spinal cord, sPLA(2)-IIC expression was high in the cerebral neocortex, hippocampus and thalamus/hypothalamus, sPLA(2)-V expression was high in the olfactory bulb and cerebellum, and sPLA(2)-X was expressed at very low levels in the normal CNS. Of the isoforms, sPLA(2)-IIA mRNA expression was highest in the brainstem and spinal cord suggesting that this could be the most relevant isoform in the ascending pain pathway. Western blot analysis showed high level of sPLA(2)-IIA expression in the brainstem and cervical, thoracic and lumbar spinal segments but low level of expression in other parts of the brain. sPLA(2)-IIA was localized by immunohistochemistry to the spinal trigeminal and facial motor nuclei and dorsal- and ventral-horns of the spinal cord. The enzyme was found on the endoplasmic reticulum of neuronal cell bodies and small diameter dendrites or dendritic spines at electron microscopy. The expression of sPLA(2)-IIA in the dorsal horn and spinal trigeminal nucleus is consistent with previous results which showed an important role of CNS sPLA(2) in nociceptive transmission.

Structural insight into the activation mechanism of human pancreatic prophospholipase A2

Pancreatic phospholipase A2 (phospholipase A2 group 1B, G1B) belongs to the superfamily of secreted phospholipase A2 (PLA2) enzymes. G1B has been proposed to be a potential target for diseases such as hypertension, obesity, and diabetes. Human pancreatic prophospholipase A2 (pro-hG1B) is activated by cleavage of the first seven-residue propeptide (phospholipase A2 propeptide, PROP). However, questions still remain on the mode of action for pro-hG1B. In this work, we expressed pro-hG1B in Pichia pastoris and determined the crystal structure at 1.55-A resolution. The x-ray structure demonstrates that pro-hG1B forms a trimer. In addition, PROP occupies the catalytic cavity and can be self-cleaved at 37 degrees C. A new membrane-bound surface and activation mechanism are proposed based on the trimeric model of pro-hG1B. We also propose a new autoproteolytic mechanism for pro-hG1B by the reaction triad Asp49-Arg0-Ser(-2) that is similar to the serine protease catalytic triad.