Extracellular proteases from haloarchaea (halolysins) can resist high salt conditions. In this study, the gene encoding a halolysin from Halococcus salifodinae was identified. The hlyA gene encoded an active halolysin with the classical Asp-His-Ser catalytic triad of serine proteases. Site-directed mutagenesis showed that the three cysteine residues in the catalytic domain were important for the extracellular proteolytic activity and displayed an additive effect on the activity. Truncation mutants of the C-terminal extension (CTE) domain displayed very low or almost no extracellular protease activity towards milk and small peptide substrates, indicating its importance for the function of HlyA. CTE can be functionally interchangeable among halolysins. Additionally, the HlyA expressing strain as a starter culture for fish sauce fermentation significantly increased the peptide release and total free amino acid content in fish sauce. This study enriches our knowledge of the key amino acid residues and domains of halolysins, and provides an opportunity for applications of halolysins in fish sauce fermentation.

来自盐古菌的细胞外蛋白酶（盐溶素）可以抵抗高盐条件。在这项研究中，鉴定了编码盐生嗜盐菌的卤溶素的基因。该靶向hlyA该基因用丝氨酸蛋白酶的经典Asp-His-Ser催化三联体编码活性卤溶素。定点诱变表明，催化域中的三个半胱氨酸残基对细胞外蛋白水解活性很重要，并显示了对活性的累加效应。C末端延伸（CTE）域的截断突变体显示出非常低或几乎没有针对牛奶和小肽底物的细胞外蛋白酶活性，表明其对HlyA功能的重要性。CTE在卤代溶素之间可以在功能上互换。另外，表达HlyA的菌株作为鱼酱发酵的起始培养物显着增加了鱼酱中肽的释放和总游离氨基酸含量。这项研究丰富了我们对卤溶素的关键氨基酸残基和结构域的了解，