Properties of recombinant novel cinnamoyl esterase from Lactobacillus acidophilus F46 isolated from human intestinal bacterium

A novel cinnamoyl esterase (CE) gene (741 bp) from Lactobacillus acidophilus F46 was cloned and expressed with a His₆-tagged protein in Escherichia coli. The recombinant CE consists of 247 amino acids and shows the highest similarity of 70% with CE sequences of Lactobacillus jonnosonii. The purified enzyme presents a single band on SDS- PAGE with an apparent molecular mass of about 27 kDa. It showed the highest activity at pH 7.5 and 50 °C. Also, it presented stability over a range of pH 4.0-9.0, and thermal stability of the enzyme decreased rapidly at temperatures above 50 °C. At a concentration of 5 mM liter^-1, CaCl₂, CuSO₄, FeSO₄, and MnSO₄ reduced the activity by 75.9, 55.4, 59.8, and 73.8% respectively, which indicates different inactivation resistance compared to other CE from lactic acid bacteria. Under standard conditions (pH 7.0 and 37 °C) with chlorogenic acid as a substrate, the enzyme exhibited a K_m of 4.89 mmol liter^-1 and V_max of 1250 μmol/min^-1 mg^-1 of protein. The purified recombinant CE showed a very strong conversion activity of chlorogenic acid to caffeic acid, and 95.3% of the chlorogenic acid was consumed. At the same time, the caffeic acid reached a concentration of 8 mM at 60 min whereas the chlorogenic acid remained the same at only 0.8 mM. This high conversion ratio of the CE from lactic acid bacteria strongly indicates that this lactic acid bacteria with strong CE enzymatic activity has the potential for industrial applications.