An aspartic-metalloprotease from an endemic plant tuber (Burnatia enneandra micheli): Purification and biochemical characterization

Abstract

Background: The objective of this work was to isolate, optimize, and characterize protease from Burnatia enneandra which is an endemic plant found abundantly in the Far-Nord Region of Cameroon. The optimum condition to extract maximum quantity of protease from B. enneandra with respect to pH, the ratio (m/v), and agitation frequency was defined as 5.1%, 4%, and 100 rpm, respectively. Materials and Methods: The enzyme was purified using ammonium sulphate precipitation, double gel filtration chromatography sephadex G200 followed by sephadex G75 and the purified protease was further characterized. With an apparent molecular weight of 23 kDa on SDS-PAGE, the purified protease showed maximum activity at 5.1 and 40°C respectively for pH and temperature. Its activity was enhanced by metal ions such as Ca2+ and Ni2+, while Fe2+and Zn2+ showed significant inhibition. Results: B. enneandra protease activity was not affected by proteases inhibitors such as phenylmethylsulfonyl fluoride, aprotinin, and iodoacetamide but was strongly inhibited by Pepstatin A and ethylenediaminetetraacetic acid which allowed to classify this new protease as aspartic-metalloproteases. Using casein as substrate, protease from B. enneandra had a maximum rate of reaction (Vmax) and Michaelis-Menten constant (Km) of 64.935 (U/mL) and 373.941 (μg/mL), respectively. Abbreviations used: CCD: Central composite design; Km: Michaelis–Menten constant; Vmax: Maximum Velocity; PBD: Plackett–Burman design; PMSF: Phenylmethylsulfonyl floride; AAD: Absolute Average Deviation; AF: Accuracy Factor; BSA : Bovine serum albumin; BF: Bias factor; EDTA: Ethylene diamine tetraacetic acid; RSM: Response surface methodology; SDS-PAGE: Sodium dodecyl sulfate polyacrylamide gel electrophoresis.