Biochemical and molecular characterization of a novel calcium-dependent metalloprotease from Bacillus cereus SV1

An extracellular calcium-dependent protease from a newly isolated Bacillus cereus SV1 was purified, characterized and the gene was isolated and sequenced. The enzyme was purified to homogeneity by ultrafiltration, Sephacryl S-200 gel filtration, DEAE-cellulose ion exchange chromatography, then by a second gel filtration on Sephacryl S-200 with a six-fold increase in specific activity and 28% recovery. The production of SV1 protease was observed in media containing CaCl2 but not in media containing BaCl2, MgCl2, MnCl2 and ZnCl2. The molecular weight of the enzyme was estimated to be 35.5 kDa on SDS-PAGE. The enzyme exhibited maximal activity at pH 8.0 and 55 °C, without the presence of CaCl2. Thermoactivity and thermostability of the enzyme were significantly increased in the presence of Ca2+. The activity was totally lost in the presence of EDTA, suggesting that the purified enzyme is a metalloprotease.The nprC1 gene, which encodes the calcium-dependent protease from B. cereus SV1, was isolated and its DNA sequence was determined. The nprC1 gene consists of 1701 bp encoding a preproprotein of 566 amino acids with three distinct domains: a signal peptide (27 amino acids), a pro-peptide (222 amino acids) and a mature enzyme (317 amino acids). The nprC1 gene coding sequence presents only 91% and 89% identity to those encoding neutral protease from B. cereus ATCC 14579 and bacillolysin from B. cereus DSM 3101, respectively. The deduced amino acid sequence of the mature protease (NprC1) differs from those of DSM 3101 and ATCC 14579 with 16 and 17 amino acids, respectively, suggesting that the nprC1 is a new protease gene.