Intracellular subtilisin proteases (ISPs) have important roles in protein processing during the stationary phase in bacteria. Their unregulated protein degrading activity may have adverse effects inside a cell， but little is known about their regulatory mechanism. Until now， ISPs have mostly been described from Bacillus species， with structural data from a single homolog. Here， we study a marine ISP originating from a phylogenetically distinct genus， Planococcus sp. The enzyme was successfully overexpressed in E. coli， and is active in presence of calcium， which is thought to have a role in minor， but essential， structural rearrangements needed for catalytic activity. The ISP operates at alkaline pH and at moderate temperatures， and has a corresponding melting temperature around 60 °C. The high-resolution 3-dimensional structure reported here， represents an ISP with an intact catalytic triad albeit in a configuration with an inhibitory pro-peptide bound. The pro-peptide is removed in other homologs， but the removal of the pro-peptide from the Planococcus sp. AW02J18 ISP appears to be different， and possibly involves several steps. A first processing step is described here as the removal of 2 immediate N-terminal residues. Furthermore， the pro-peptide contains a conserved LIPY/F-motif， which was found to be involved in inhibition of the catalytic activity.