A catalytically inactive Lys49 PLA2 isoform from Bothrops jararacussu venom that stimulates insulin secretion in pancreatic beta cells.

A new secretory phospholipase A2 (sPLA2) isoform from Bothrops jararacussu venom (BjVIII) has been characterized by causing platelet aggregation, an absent activity in BthTx-I, Prtx-I and PrTx-II sPLA2s. According to our results, BjVIII also enhances insulin release by the pancreatic beta cells. The complete amino acid sequence of the new isoform was determined by Edman degradation and de novo peptide sequencing. These analyses showed a G35K amino acid modification for BjVIII in comparison with BthTx-I, PrTx-I and Prtx-II, a structural difference that has been related to the conflicting biological activities among BjVIII and other Lys49 sPLA2s. The whole set of evidences collected in this work indicates that, besides the C-terminal region and B-wing of PLA2, the calcium binding loop in BjVIII should be considered as an important region, involved in the pharmacological effects of Lys49-sPLA2 isoforms from the Bothrops genus.

Modulation of the pharmacological activities of secretory phospholipase A2 from Crotalus durissus cascavella induced by naringin.

In this work we have characterized the action of the naringin, a flavonoid found in grapefruit and known for its various pharmacological effects, which include antioxidant blood lipid lowering and anticancer activity, on the structure and biochemical activities of a secretory phospholipase A (sPLA2) from Crotalus durissus cascavella, an important protein involved in the releasinge of arachidonic acid in phospholipid membranes. sPLA2 was incubated with naringin (mol:mol) at 37 °C and a discrete reduction in the UV scanning signal and a modification of the circular dichroism spectra were observed after treatment with naringin, suggesting modifications of the secondary structure of the protein. This flavonoid was able to decrease enzymatic activity and some pharmacological effects, such as myonecrosis, platelet aggregation, and neurotoxic activity caused by sPLA2, however, the inflammatory effect was not affected by naringin. In addition, small angle X-ray scattering (SAXS) data were collected for sPLA2 and naringin-treated sPLA2 to evaluate possible modifications of the protein structure. These structural investigations have shown that sPLA2 is an elongated dimer in solution and after treatment with naringin a conformational change in the dimeric configuration was observed. Our results suggest that structural modification may be correlated with the loss of enzymatic activity and alterations in pharmacological properties.