Extracellular proteases from halophilic archaea displays increased enzymatic activities in hypersaline environment. In this study, an extracellular protease-coding gene, hly34, from the haloarchaeal strain Halococcus salifodinae PRR34, was obtained through homologous search. The protease activity produced by this strain at 20% NaCl, 42 °C, and pH 7.0 was 32.5 ± 0.5 (U·mL⁻¹). The codon-optimized hly34 which is specific for Escherichia coli can be expressed in E. coli instead of native hly34. It exhibits proteolytic activity under a wide range of low- or high-salt concentrations, slightly acidic or alkaline conditions, and slightly higher temperatures. The Hly34 presented the highest proteolytic activity at 50 °C, pH 9.0, and 0–1 M NaCl. It was found that the Hly34 showed a higher enzyme activity under low-salt conditions. Hly34 has good stability at different NaCl concentrations (1–4 M) and pH (6.0–10.0), as well as good tolerance to some metal ions. However, at 60 °C, the stability is reduced. It has a good tolerance to some metal ions. The proteolytic activity was completely inhibited by phenylmethanesulfonyl fluoride, suggesting that the Hly34 is a serine protease. This study further deepens our understanding of haloarchaeal extracellular protease, most of which found in halophilic archaea are classified as serine proteases. These proteases exhibit a certain level of alkaline resistance and moderate heat resistance, and they may emerge with higher activity under low-salt conditions than high-salt conditions. The protease Hly34 is capable of degrading a number of proteins, including substrate proteins, such as azocasein, whey protein and casein. It has promising applications in industrial production.

来自嗜盐古菌的细胞外蛋白酶在高盐环境中表现出增强的酶活性。本研究通过同源检索，从盐古菌菌株Halococcus salifodinae PRR34中获得了一个胞外蛋白酶编码基因hly34 。该菌株在20% NaCl、42℃、pH 7.0下产生的蛋白酶活性为32.5±0.5(U·mL ^-1 )。大肠杆菌特异的密码子优化的hly34可以在大肠杆菌中表达，而不是天然的hly34 。它在各种低或高盐浓度、微酸性或碱性条件以及稍高的温度下表现出蛋白水解活性。 Hly34 在 50 °C、pH 9.0 和 0–1 M NaCl 下表现出最高的蛋白水解活性。结果发现，Hly34在低盐条件下表现出较高的酶活性。 Hly34在不同的NaCl浓度（1-4M）和pH（6.0-10.0）下具有良好的稳定性，并且对某些金属离子具有良好的耐受性。然而，在 60°C 时，稳定性会降低。对某些金属离子有良好的耐受性。苯甲磺酰氟完全抑制蛋白水解活性，表明Hly34 是一种丝氨酸蛋白酶。这项研究进一步加深了我们对盐古菌胞外蛋白酶的认识，嗜盐古菌中发现的大多数胞外蛋白酶被归类为丝氨酸蛋白酶。这些蛋白酶表现出一定程度的耐碱性和中等耐热性，并且它们在低盐条件下可能比高盐条件下具有更高的活性。蛋白酶 Hly34 能够降解多种蛋白质，包括底物蛋白质，例如偶氮酪蛋白、乳清蛋白和酪蛋白。 在工业生产中具有广阔的应用前景。