Propriedades Bioquímicas e Funcionais de uma Proteína Ligante à Quitina Purificada de Sementes de Moringa oleifera Lamarck

Abstract

Moringa oleifera Lam. is native from Northwest India, well adapted to tropical regions. From its seeds it was isolated a new chitin binding protein, Mo-CBP3, which has coagulant properties and antifungal activity against the phytopathogen Fusarium solani. Proteins were extracted from defatted seeds flour by 0.05 M Tris-HCl buffer, pH 8.0, containing 0.15 M NaCl. The average protein content of the flour was 216.44 mgP/gF. The crude extract was fractionated in albumins and globulins by dialysis and centrifugation. Albumins were concentrated by 90% ammonium sulfate saturation. This fraction was applied into a chitin column, previously equilibrated with the same buffer. An unadsorbed and two adsorbed peaks were obtained. The first adsorbed peak was eluted with 0.1 M N-acetyl-D-glucosamine (PNAG), and the second one, with 0.05 M acetic acid, pH 3.0 (PAC). PNAG was applied into a cation exchange column, Resource S, equilibrated with 0.05 M sodium acetate buffer, pH 5.2. The third peak corresponded to Mo-CBP3 – eluted with 0.5 M NaCl in equilibrium buffer. The protein content of Mo- CBP3 was 1.17 mgP/gF. It represents a final yield of 0.54% of crude extract proteins. Apparent molecular mass by SDS-PAGE was 18.0 kDa in the absence of β-ME, and 9.0 kDa, in its presence. Results suggest that Mo-CBP3 is a dimeric protein, made of identical subunits, linked by disulfide bonds. By molecular exclusion chromatography, calculated molecular mass was 14.34 kDa, pI 10.8. Mo-CBP3 is a glycoprotein with 2.5% of carbohydrates, which has not hemagglutinating or chitinase activities. Its NH2- terminal sequence was CPAIQRCCQQLRNIQPPCRCCQ, with 22 amino acids, conffirming its basic character. Mo-CBP3 was as efficient as AlK(SO4)2 in the capacity of coagulating suspended material in water. Mo-CBP3 (0.1 mg/mL) was fungicide to Fusarium solani spores. Heat treatment of the protein at 98 °C, du ring 1 h, and pre incubation with N-acetyl-D-glucosamine, did not reverse its action. Mo-CBP3 was able to retard the mycelial growth of the fungus even at the lowest tested dose of 0.05 mg/mL. Mo-CBP3 was inactive against the oomycete Pythium oligandrum, which has cellulose in spite of chitin in cell wall. Protein was also able to inhibit about 80% of medium acidification, induced by glucose, by F. solani spores, that suggests the influence of Mo-CBP3 over the proton pumps (H+ATPases) present in cellular membranes of F. solani spores.