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Dominique Missiakas, Ph.D.Bacterial Physiology and PathogenesisResearch SummaryDr. Missiakas’ research program examines various protein secretion pathways of Staphylococcus aureus and Bacillus anthracis and their contribution to virulence. Recently, Dr. Missiakas and colleagues have shown that the human pathogen S. aureus secretes EsxA and EsxB across the bacterial envelope. Further, mutants that fail to secrete EsxA and EsxB display defects in the pathogenesis of S. aureus murine abscesses, suggesting that secretion of these factors is important for dissemination and colonization of S. aureus in infected animals. EsxA and EsxB are secreted by a specialized secretion system referred to as Ess, for ESAT-6 like secretion system. ESAT-6 ( early secreted an tigen of 6 kDa) was first identified along with genes required for its secretion in Mycobacterium tuberculosis. Although ESAT-6 like genes have been identified in the sequenced genomes of various Gram positive bacteria, the possibility that they might be elements of a new secretion system and contribute virulence strategies, had hitherto not been addressed.Dr. Missiakas developed bursa aurealis, a mariner based transposon that is used to generate insertion mutations in S. aureus and B. anthracis. In particular, she used bursa aurealis to create the Phoenix library, a collection of 11,000 defined insertion mutants in S. aureus strain Newman. A total of 1,853 open reading frames have been disrupted to date i.e. 70% of all genes. Phoenix is used to identify factors required for infection, regulation of toxins, study dedicated pathways such Ess-dependent secretion, heme iron uptake or protein sorting and secretion in the envelope of staphylococci. Sorting of lipoproteins has been examined in details. The pathway for lipoprotein maturation in conserved in staphylococci. Lipoproteins are synthesized in the cytoplasm as precursors with an N-terminal signal peptide for secretion via the Sec pathway. Lipoprotein diacylglycerol transferase (Lgt) catalyzes transfer of phosphatidylglycerol to the sulfhydryl moiety of a cysteine residue conserved in the signal peptides of all lipoprotein precursors. Leader signal peptidase B (Lsp) cleaves acylated precursor lipoproteins to generate matured lipoproteins. The Phoenix library was used to examine the contribution of staphylococcal lipoproteins to immune recognition and disease pathogenesis. Binding of bacterial molecules called PAMPs for pathogen associated molecule patterns, to dedicated Toll-like receptors (TLRs) or Nod proteins triggers specific signaling events and host responses to invading pathogens. Among PAMPS are gram positive bacterial lipoproteins, peptidoglycan, lipotheichoic acid, teichoic acid. The Phoenix library was examined for mutants with defects in the biosynthesis of specific PAMPs. However, only transposon insertions in lgt and lsp were identified in the Phoenix collection as the other pathways for PAMPS biosynthesis are essential for bacterial growth. S. aureuslgt mutant variants bearing apo-lipoproteins were found to escape immune recognition and cause disseminated abscess formation with increased lethality during infection. Immune cells did not infiltrate sites of infection carrying these mutant bacteria in part because TLR-2 signaling did not occur and lgt mutants did not induce production of TNF-α, IL-1 or IL-6 during infection. S. aureuslsp mutant variants bearing uncleaved acylated lipoproteins were less virulent during infection. Hence, acylation of lipoproteins is required for initiating and sustaining effective immune responses during staphylococcal infection.
Selected PapersBae T, Banger AK, Wallace A, Glass EM, Aslund F,
Schneewind O, Missiakas DM. (2004). Staphylococcus aureus virulence
genes identified by bursa aurealis mutagenesis and nematode killing.
Proc. Natl. Acad. Sci. USA 101:12312-12317. Williams WA, Zhang R-G, Zhou M, Joachimiak G, Gornicki
P, Missiakas DM, and Joachimiak A. (2004). Three-Dimensional Structure
of GmpC, the Membrane Associated Lipoprotein-9 from Staphylococcus
aureus, in Complex with Dipeptide GlyMet Defines a New Substrate
Binding Protein. Biochemistry 43, 16193-16202. Burts ML, Williams WA, DeBord KL, and Missiakas DM.
(2005). EsxA and EsxB are secreted by an ESAT-6-like system that is
required for the pathogenesis of Staphylococcus aureus infections.
Proc. Natl. Acad. Sci. 102, 1169-1174. Bubeck Wardenburg J, Williams WA, and Missiakas DM.
(2006). Host defenses against Staphylococcus aureus infection require
recognition of bacterial lipoproteins. Proc. Natl. Acad. Sci. 103,
13831-13836. |
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