Purification and characterization of a chitinase (sAMC) with antifungal activity from seeds of Astragalus membranaceus

A chitinase (sAMC) was purified from the seeds of Astragalus membranaceus (Fisch.) Bunge, using a combination of 20-60% ammonium sulfate precipitation, regenerated chitin affinity column and Sephadex G-75. Purified chitinase was a monomer with a molecular mass of 35.5 kDa on SDS-PAGE. Based on the homology search of amino acid sequences of four internal peptides, sAMC belongs to glycosyl hydrolase (GH) family 19 chitinases which are mostly endochitinases. The optimal pH of sAMC was 5.0, and it was stable over a broad range of pH 4.0-8.0. sAMC exhibited an optimal temperature of 60 °C and it was stable up to 60 °C. sAMC hydrolyzed colloidal chitin into chitotriose, chitobiose and N-acetyl d-glucosamine suggesting its role in conversion of chitin wastes into useful products. It exhibited antifungal activity against Trichoderma viride, Botrytis cinerea, Fusarium oxysporum and Fusarium solani. This is the first report on chitinases from Astragalus sp.