Secretion of T at‐dependent halolysin S pt A capable of autocatalytic activation and its relation to haloarchaeal growth

Summary Halolysins are T at‐dependent extracellular subtilases of haloarchaea. Whether halolysins can be activated before transport across the cytoplasmic membrane in a folded state and how haloarchaea minimize the risk of intracellular activation of halolysins and proteolysis of cellular proteins are unknown. Here, we report that both the precursor and proform of halolysin S pt A from N atrinema sp. J 7‐2 mature autocatalytically, and the S pt A maturation proceeds less efficiently in the presence of KCl than N a C l. When produced in H aloferax volcanii , most S pt A molecules are secreted into the culture medium, but a small number of molecules can be activated intracellularly, affecting the cell's growth. Furthermore, retardation of S pt A secretion in H fx. volcanii via mutation of the T at signal peptide leads to intracellular accumulation of the active enzyme and subsequent cell death. Although the S ec signal peptide can mediate S pt A secretion in H fx. volcanii , the secreted protein undergoes proteolysis. In N atrinema sp. J 7‐2, S pt A is secreted primarily during stationary phase, and the intracellular accumulation of mature enzyme occurs during the stationary and death phases. The growth phase‐dependent synthesis of S pt A , highly efficient secretion system, and high intracellular KC l concentration, contribute to the suppression of premature activation of this enzyme in N atrinema sp. J 7‐2.