A novel serine metalloprotease from a newly isolated Lactococcus lactis subsp. Lactis BR16 : Purification and characterization

An extracellular metalloprotease producing strain was isolated from Algerian traditional fermented food and identified as Lactococcocus lactis subsp. Lactis BR16 on the basis of the16SrRNA gene sequencing with accession number AB618806.1 and biochemical properties. The BR16 metalloprotease was purified from the culture supernatant to homogeneity using ultrafiltration, SP-Sepharose ion exchange chromatography Sephadex G-50 gel filtration, with a 5.83-fold increase in specific activity and 47% recovery. The molecular weight of the purified enzyme was estimated to be 38 kDa by SDS-PAGE and gel filtration. The enzyme was highly active over a wide range of pH from 5.0 to 8.0, with an optimum at pH 6.5. The relative activities at pH 6.0 and 7.5 were about 94% and 90% of that obtained at pH 6.5. The enzyme was extremely stable in the pH range of 5.0-9.0. It exhibited maximal activity at 55 °C. The activity of the enzyme was totally lost in the presence of phenantroline, suggesting that the purified enzyme is a metalloprotease. Reversed-phase high performance liquid chromatography (RP-HPLC) of commercial casein digests showed a more-complex peptide pattern produced by the proteinase of Lactococcus lactis subsp lactis BR16.