Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia

The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of Serratia grimesii and protealysin of Serratia proteamaculans, characterized by both a highly specific “actinase” activity and their ability to stimulate bacterial invasion. Grimelysin cleaves the only polypeptide bond Gly42-Val43 in actin. This bond is not cleaved by any other proteases and leads to a reversible loss of actin polymerization. Similar properties were characteristic for another bacterial protease, protealysin. These properties made grimelysin and protealysin a unique tool to study the functional properties of actin. Furthermore, bacteria Serratia grimesii and Serratia proteamaculans, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant Escherichia coli expressing the grimelysin or protealysins gene become invasive. Participation of the cellular c-Src and RhoA/ROCK signaling pathways in the invasion of eukaryotic cells by S. grimesii was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by S. grimesii were found to contain grimelysin, penetrate into eukaryotic cells and increase the invasion of bacteria into eukaryotic cells. These data indicate that the protease is a virulence factor, and actin can be a target for the protease upon its translocation into the host cell.