Autoproteolytic activation of the haloalkaliphilic archaeon Natronococcus occultus extracellular serine protease

The haloalkaliphilic archaeon Natronococcus occultus produces an extracellular serine protease in the stationary growth phase and upon starvation. Two proteins immunologically related to the extracellular protease were detected into the cells: P200 and P190. P200 was detected at early stages of growth and its relative amount decreased as the culture reached the stationary growth phase, concomitantly with the appearance of P190 and proteolytic activity, suggesting that P200 may be the precursor of the secreted protease and P190 the mature enzyme. Both proteins were also detected in the culture medium. Conversion of inactive P200 into active P190 was attained in cell-free culture medium from stationary phase but not from exponential phase. This process was prevented in the presence of PMSF and could be attained by addition of purified mature extracellular protease to P200. Altogether these results indicate that activation of Natronococcus occultus extracellular protease may be autoproteolytic and that factor/s present in stationary phase culture medium may be required for this process.