A novel halolysin from haloarchaeon Natrialba sp. strain PRR66: identification and characterization

In this study, the hly66 encoding an extracellular protease was cloned from the haloarchaeon Natrialba sp. PRR66 and achieved its successful heterologous expression in Escherichia coli. The enzyme activity can be abolished by phenylmethylsulfonyl fluoride (PMSF). The recombinant protein MBP-Hly66 (rHLY66) exhibits the maximum enzymatic activity under high temperature, high-salinity and alkaline conditions (60 °C, pH 9.0 and 4.0 M NaCl), a characteristic that fulfills the requirements of specialized industrial applications. The kinetics of halolysin rHLY66 including K_m, V_max and K_cat were determined to be 1.79 mM, 751.28 U mg^-1 and 1502.56 S^-1, respectively, using azocasecin as substrate. Moreover, rHLY66 demonstrates enhanced stability and low-salt adaptability compared to conventional halolysins. This unique low-salt tolerance enables the enzyme to function effectively across a wider salinity range, highlighting its potential for diverse applications in the salt-fermented food industry.