A new thermostable rhizopuspepsin: Purification and biochemical characterisation

Abstract

The new thermostable fungal aspartic protease was produced through solid-state fermentation from Rhizopus azygosporus (MTCC 10195). The protease was purified by a three-tandem steps of ammonium sulfate precipitation (25−65 % saturation), ion exchange (DEAE sepharose CL 6B) chromatography, and gel filtration (Sephacryl S 200) chromatography. The optimum pH and temperature for protease activity were 4 and 52 ± 1.8 °C, respectively. The enzyme was unusually thermostable, as it retained 50 % of its activity beyond 85 °C after 20 min of incubation. The apparent molecular weight was 33.2 ± 2.3 kDa with a final specific activity of 86.6 U/mg. The enzyme was rich in β sheets (63 %) and was inhibited by pepstatin A, indicating that it is an aspartic protease. MS/MS analysis revealed the enzyme is an endopeptidase cleaving the C-terminus of Phe, Leu, Lys, Val, His, Glu, Met, and Tyr. Amino-terminal sequencing, coupled with in-gel trypsin digestion and MS analysis revealed that the enzyme was being reported for the first time with “experimental evidence at protein-level”.