2D proteome analysis initiates new Insights on the <it>Salmonella </it>Typhimurium LuxS protein

<p>Abstract</p> <p>Background</p> <p>Quorum sensing is a term describing a bacterial communication system mediated by the production and recognition of small signaling molecules. The LuxS enzyme, catalyzing the synthesis of AI-2, is conserved in a wide diversity of bacteria. AI-2 has therefore been suggested as an interspecies quorum sensing signal. To investigate the role of endogenous AI-2 in protein expression of the Gram-negative pathogen <it>Salmonella enterica </it>serovar Typhimurium (<it>S</it>. Typhimurium), we performed a 2D-DIGE proteomics experiment comparing total protein extract of wildtype <it>S</it>. Typhimurium with that of a <it>luxS </it>mutant, unable to produce AI-2.</p> <p>Results</p> <p>Differential proteome analysis of wildtype <it>S</it>. Typhimurium versus a <it>luxS </it>mutant revealed relatively few changes beyond the known effect on phase 2 flagellin. However, two highly differentially expressed protein spots with similar molecular weight but differing isoelectric point, were identified as LuxS whereas the <it>S</it>. Typhimurium genome contains only one <it>luxS </it>gene. This observation was further explored and we show that the <it>S</it>. Typhimurium LuxS protein can undergo posttranslational modification at a catalytic cysteine residue. Additionally, by constructing LuxS-βla and LuxS-PhoA fusion proteins, we demonstrate that <it>S</it>. Typhimurium LuxS can substitute the cognate signal peptide sequences of β-lactamase and alkaline phosphatase for translocation across the cytoplasmic membrane in <it>S</it>. Typhimurium. This was further confirmed by fractionation of <it>S</it>. Typhimurium protein extracts, followed by Western blot analysis.</p> <p>Conclusion</p> <p>2D-DIGE analysis of a <it>luxS </it>mutant <it>vs</it>. wildtype <it>Salmonella </it>Typhimurium did not reveal new insights into the role of AI-2/LuxS in <it>Salmonella </it>as only a small amount of proteins were differentially expressed. However, subsequent in depth analysis of the LuxS protein itself revealed two interesting features: posttranslational modification and potential translocation across the cytoplasmic membrane. As the <it>S</it>. Typhimurium LuxS protein does not contain obvious signal motifs, it is speculated that LuxS is a new member of so called moonlighting proteins. These observations might have consequences in future studies on AI-2 quorum signaling in <it>S</it>. Typhimurium.</p>

Abstract licence: CC BY-NC-ND

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