THE STORY ON AN INTRIGUING ACTIN-SPECIFIC PROTEASE THAT TURNED OUT TO BE GRIMELYSIN, A MEMBER OF A RESPECTABLE FAMILY
OF THERMOLYSIN-LIKE METALLOPROTEINASES
S. Yu. Khaitlina
Institute of Cytology RAS, St. Petersburg;
e-mail: skhspb@yahoo.com
The article describes a story of the discovery and properties of bacterial metalloproteinase ECP32 that cleaves actin at the only site between Gly42 and Val43.
This site is intensively involved in the monomer-monomer contacts within actin filament. Cleavage with ECP32 results in a reversible loss of actin polymerizability.
Therefore ECP cleaved actin has been a unique model to study mechanisms of actin polymerization and the filament dynamics, and the effects of actin-binding
proteins on these processes, as well as to reveal allosteric effects in actin molecule and to determine three-dimensional actin structure that was previously
determined only for the actin-ligand complexes. Furthermore, the non-pathogenic bacteria synthesizing ECP32 were shown to penetrate in eukaryotic cells
rearranging their cytoskeleton. Biochemical analysis using the Vitek-2 system and sequencing of the 16S rRNA gene reidentified the ECP32-producing strain,
previously identified as E. coli, as Serratia grimesii. Bacteria of a reference strain S. grimesii were found to express the gene of metalloprotease
that cleaves actin similarly to ECP32. The gene was cloned, sequenced and expressed in E. coli. The protein encoded by this gene was named grimelysin.
Grimelysin shared essential characteristics of ECP32: molecular weight, limited actin proteolysis, inhibition by chelating agents, cleavage site, and the N-terminal
amino acids of the active enzyme published for ECP32. These data show that grimelysin and ECP32 seem to be the same protein. As it was demonstrated by
confocal microscopy the bacteria capable of synthesizing natural or recombinant grimelysin acquire invasive phenotype. The data described here allow us to
suggest that actin may be a target protein which proteolysis promotes bacterial invasion.
Key words: actin, actin proteolysis, metalloproteinases, protease ECP32, grimelysin, bacterial invasion
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