Cleavage of the outer membrane protein OmpX by protealysin regulates Serratia proteamaculans invasion

Protealysin is a thermolysin-like protease of Serratia proteamaculans capable of specifically cleaving actin, which correlates with the invasive activity of these bacteria. Here, we show that inactivation of the protealysin gene does not inhibit invasion but, in contrast, leads to a twofold increase in the S. proteamaculans invasive activity. By mass spectrometry, we identified the outer membrane protein OmpX as a substrate of protealysin. Recombinant E. coli carrying the OmpX gene truncated by 40 N-terminal residues or both the OmpX and protealysin genes, in contrast to the full-length OmpX, do not increase adhesion of these bacteria, indicating that the 40 N-terminal residues of OmpX are indispensable for S. proteamaculans invasion. Our results show that both protealysin and its substrates can stimulate Serratia invasion.