Purification and biochemical characterization of a secreted group IIA chicken intestinal phospholipase A₂.

BACKGROUND

Secretory phospholipase A2 group IIA (IIA PLA2) is a protein shown to be highly expressed in the intestine of mammals. However, no study was reported in birds.

RESULTS

Chicken intestinal group IIA phospholipase A₂ (ChPLA₂-IIA) was obtained after an acidic treatment (pH.3.0), precipitation by ammonium sulphate, followed by sequential column chromatographies on Sephadex G-50 and mono-S ion exchanger. The enzyme was found to be a monomeric protein with a molecular mass of around 14 kDa. The purified enzyme showed a substrate preference for phosphatidylethanolamine and phosphatidylglycerol, and didn't hydrolyse phosphatidylcholine. Under optimal assay conditions, in the presence of 10 mM NaTDC and 10 mM CaCl₂, a specific activity of 160 U.mg⁻¹ for purified ChPLA₂-IIA was measured using egg yolk as substrate. The fifteen NH2-terminal amino acid residues of ChPLA₂-IIA were sequenced and showed a close homology with known intestinal secreted phospholipases A₂. The gene encoding the mature ChPLA₂-IIA was cloned and sequenced. To further investigate structure-activity relationship, a 3D model of ChPLA₂-IIA was built using the human intestinal phospholipase A₂ structure as template.

CONCLUSION

ChPLA2-IIA was purified to homogeneity using only two chromatographic colomns. Sequence analysis of the cloned cDNA indicates that the enzyme is highly basic with a pI of 9.0 and has a high degree of homology with mammalian intestinal PLA₂-IIA.