Extracellular zinc metalloprotease. Preferential cleavage: Xaa-|-Leu > Xaa-|-Phe. Binds 4 Ca(2+) ions per subunit. Binds 1 zinc ion per subunit. Thermostable. Retains about 45% of its activity after treatment of 90 degrees Celsius for 30 minutes. Is expressed in the stationary phase. Up-regulated by NprA. Belongs to the peptidase M4 family.