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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