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TTSS effectors of plant pathogenic bacteria acting as SUMO-specific proteases

Area: SUMO proteases as bacterial virulence proteins
Leader/s: Javier Ruiz Albert
Members:

Javier Ruiz Albert
Carmen R. Beuzón López

Eduardo Rodríguez Bejarano

Description:
This research line pursues the molecular characterization of TTSS effector proteins from several phytopathogenic bacteria, belonging to the C55 family of SUMO-specific proteases. We aim to confirm their specific activity both in vitro and in vivo, to identify their interacting partners in planta, to analyse their role in the infectious process, and to determine their contribution to virulence or to the induction of plant defense reactions.

Sumoylation constitutes a post-translational modification process, recently discovered in eukaryotic organisms, which implies the covalent binding to certain proteins of an small peptide similar to ubiquitin, designated SUMO (small ubiquitin-like modifier). Sumoylation affects many eukaryotic proteins involved in numerous celular processes, and can influence protein-protein or DNA-protein interaction, enzymatic activity, or even subcellular localisation. The sumoylation levels of cellular proteins are dinamically maintained through the balanced action of SUMO-conjugating enzymes and SUMO-specific proteases, the latter able to break the covalent bond between the sumoylated proteins and SUMO. The SUMO proteases are also required to activate SUMO, which is produced as a propeptide requiring proteolytic processing prior to its attachment to the target proteins.

Current experimental data obtained in animal and plant systems strongly suggests that sumoylation is involved in host responses to bacterial, viral, and fungal infections. There is also mounting evidence that some pathogens are able to interfere with the sumoylation systems of their hosts, in a variety of manners. Many pathogenic bacteria secrete virulence-associated proteins directly into the cytosol of the eukaryotic host cell by means of Type III Secretion Systems (TTSS). Each individual bacterial strain posses a specific ensemble of TTSS-secreted proteins (also called effectors), which are functionally quite diverse and collectively contribute to bacterial virulence. Among these bacterial effectors a family of proteins (MEROPS C55) share significant sequence similarity with eukaryotic SUMO-specific proteases, particularly in the catalytic domain. At least fifteen members of this family have been described in plant pathogenic strains of Xanthomonas, Pseudomonas, Ralstonia or Erwinia. The SUMO-specific protease activity on plant substrates has already been shown for three of the Xanthomonas effectors, with the rest pending characterisation. To date, the target proteins in the plant cell for any of these effectors have not been identified.



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