Trypsin inhibitor isolated from Streptomyces misionensis UMS1 has anti-bacterial activities and activates α-amylase

Protease inhibitors (PI) discovered to be widely distributed in animals, plants and microorganisms, but the information on bacterial PI is scarce. Trypsin inhibitor, named SMTI, was purified from local actinomycete strain (Kuala Lumpur, Malaysia), Streptomyces misionensis UMS1, by acetone precipitation and trypsin-agarose affinity chromatography. Reverse-phase HPLC did not reveal isoinhibitor in purified PI. The purification resulted in a 14 kDa protein, visualized on SDS-PAGE and analyzed with MALDITOF/ TOF. Isoelectric focusing of SMTI demonstrated a single protein with an acidic pI of 6.2. SMTI showed inhibitory activity towards trypsin (74%) and chymotrypsin (41%). Kinetic analysis of trypsin inhibitory activity of SMTI revealed a competitive mechanism with an inhibition constant, Ki of 5 × 10–7 M. SMTI was also shown to have a significant ability to enhance the acitivity of α-amaylase (47%). Furthermore, SMTI exhibited an antibacterial activity against Bacillus cereus , Erwinia , Ralstonia , Salmonella typhi , and Escherichia coli with MIC of 0.06, 0.06, 0.015, 0.12, and 0.48 mg/mL, respectively