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The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of <i>Serratia grimesii</i> and protealysin of <i>Serratia proteamaculans</i>, 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 <i>Serratia</i> <i>grimesii</i> and <i>Serratia proteamaculans</i>, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant <i>Escherichia coli</i> 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 <i>S. grimesii</i> was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by <i>S. grimesii</i> 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.