Genetic and biochemical properties of an extracellular neutral metalloprotease from Staphylococcus hyicus subsp. hyicus

The gene encoding the extracellular neutral metalloprotease ShpI from Staphylococcus hyicus subsp. hyicus was cloned. DNA sequencing revealed an ORF of 1317 nucleotides encoding a 438 amino acid protein with Mr of 49698. When the cloned gene was expressed in Staphylococcus carnosus, a 42 kDa protease was found in the culture medium. The protease was purified from both S. carnosus (pCAshp1) and S. hyicus subsp. hyicus. The N-terminal amino acid sequences of the two proteases revealed that ShpI is organized as a pre-pro-enzyme with a proposed 26 amino acid signal peptide, a 75 amino acid hydrophilic pro-region, and a 337 amino acid extracellular mature form with a calculated Mr of 38394. The N-termini showed microheterogeneity in both host strains. ShpI had a maximum proteolytic activity at 55°C and pH 7.4–8.5. The protease, which had a low substrate specificity, could be inhibited by metal- and zinc-specific inhibitors, such as EDTA and 1,10-phenanthroline. Insensitivity to phosphoramidon separates ShpI from the thermolysin-like family. The conserved Zn²⁺ binding motif, the only homology to other proteases, and the reactivation of the apoenzyme by Zn²⁺, indicated that Zn²⁺ is the catalytic ion. Ca²⁺ very probably acts as a stabilizer. We also demonstrated the presence of a second extracellular protease in S. hyicus subsp. hyicus.