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SseL, a Salmonella deubiquitinase required for macrophage killing and virulence

  • Anne Rytkönen
  • John Poh
  • Junkal Garmendia
  • Cliona Boyle
  • Arthur Thompson
  • Mei Liu
  • Paul Freemont
  • Jay C. D. Hinton
  • David W. Holden
National Academy of Sciences
Publication Date
Feb 20, 2007
  • Biology


Expression of the Salmonella enterica serovar Typhimurium pathogenicity island 2 (SPI-2) type III secretion system is controlled by the two-component regulatory system SsrA-SsrB. We used a transcriptomic approach to help define the SsrA-SsrB regulon. We identified a gene encoding an uncharacterized effector (SseL) whose translocation into host cells depends on the SPI-2 secretion system. SseL has similarities to cysteine proteases with deubiquitinating activity. A GST-SseL fusion protein specifically hydrolyzed mono- and polyubiquitin substrates in vitro with a preference for K63-linked ubiquitin chains. Ubiquitin-modified proteins accumulated in macrophages infected with Salmonella sseL mutant strains but to a lesser extent when infected with bacteria expressing active protein, demonstrating that SseL functions as a deubiquitinase in vivo. Salmonella sseL mutant strains did not show a replication defect or induce altered levels of cytokine production upon infection of macrophages but were defective for a delayed cytotoxic effect and were attenuated for virulence in mice.

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