Purification and characterization of a novel heterodimer protease inhibitor from Streptomyces spp. VL J2 with potential biopesticidal activity against H. armigera

•A new heterodimeric proteinaceous protease inhibitor of approximately 38 kD was isolated from salt tolerant haloalkaliphilic Streptomyces spp.•The purified protease inhibitor was found to be stable over a wide range of pH and temperature.•The molecular weight, amino acids/groups required for activity and protease inhibition profile indicated it to be a serine protease inhibitor probably belonging to the serpin family.•Kinetic data showed the nature of inhibition of trypsin by it to be non competitive type with a low inhibition constant.•The isolated PI showed very good insecticidal activity against the polyphagous insect pest, Helicoverpa armigera affecting various stages of its life cycle and nutritional indices.

A protease inhibitor (PI) was isolated and purified from halo-alkaliphilic Streptomyces spp. VL J2. SDS-PAGE of purified PI revealed it to be a heterodimer of two unidentical subunits of 27.5 and 11.08 kDa, which corroborates well with intact molecular mass of 38.5 kDa obtained by GPC and MALDI −TOF. Inhibitory activity was confirmed by activity staining and reverse zymogram studies and the inhibitor was found to retain activity at <50 °C and pH 2-9.5. It showed presence of two isoforms with isoelectric point of 5.5 and 5.7. The inhibition of trypsin and chymotrypsin indicated it to be a serine protease type belonging to serpin family. The stoichiometry of trypsin-inhibitor interaction was 1:2. Modification of amino acid showed presence of arginine and free sulfhydryl group at active site. Kinetic studies revealed the non-competitive type of inhibition of trypsin with low Ki value (9.4 × 10−9 M). Activity against H. armigera showed significant decline and delay in larval (51%), pupal weights and periods, respectively, prominent physical abnormalities and reduced nutritional indices as a function of treatment. The results suggest that the purified PI has promising pesticidal activity and could serve as a potential candidate gene for transgenic plant research.

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