A novel halolysin without C-terminal extension from an extremely halophilic archaeon

Halolysins are extracellular proteases secreted by halophilic archaea for nutritional purposes. They bear great application potentials in various industries. Yet the diversity of halolysins remains underexplored. In this study, a halolysin from the extremely halophilic archaeon Haladaptatus sp. DYF46 (Hly(Hap)) was identified to be a novel type of halolysin without C-terminal extension (CTE). Addition of the CTE of a halolysin from Halococcus salifodinae to Hly(Hap) did not significantly affect its extracellular proteolytic activity. Mature Hly(Hap) was generated from recombinant Hly(Hap) precursor by high-affinity column refolding. Hly(Hap) displayed optimal activity at 0.25-0.50 M NaCl, 45 degrees C and pH 8.5-9.0. Interestingly, Hly(Hap) preferred a low salinity and was stable in a broad range of salinity, albeit from an extremely halophilic archaeon. Ca2+ and Mg2+ significantly promoted Hly(Hap) activity. Hly(Hap) activity was stable with organic solvents and detergents. The K-m and V-max values of Hly(Hap) against azocasein were 0.018 mM and 7,179 U/mg, and those against succinyl-Ala-Ala-Pro-Phe-pNA were 0.32 mM and 3x10(6) mu mol/min/mu g, respectively. The unusual traits of Hly(Hap), a novel type of halolysin without CTE, may endow it with strong potential for various industrial uses, such as biocatalysis in fluctuating salinities and aqueous-organic solvent.

Automated summary

This study identified a novel type of halolysin (Hly(Hap)) without C-terminal extension (CTE) from the extremely halophilic archaeon Haladaptatus sp. DYF46. Hly(Hap) exhibited stability and optimal activity in a low salinity condition despite being derived from an extremely halophilic archaeon. It was also found that Ca2+ and Mg2+ significantly promoted the activity of Hly(Hap). Moreover, Hly(Hap) showed stability in the presence of organic solvents and detergents.