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Immune system o facilitate adhesion of bacterium to

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immune systemofacilitate adhesion of bacterium tosubstrate or tissueosequester iron from the externalenvironmentoaid in the assembly of motilitystructuresGram-Positive Sortase SystemSortase System: mechanism that Gram-positive bacteria use to move large molecules onto their cell surfacesmodifiesSortase protein substrates andattaches themto the peptidoglycan on the cell surfaceseveral different types of Sortase enzymes that process different proteinsSrtASortase is the most conserved (similar across species)oresponsible for displaying substrates involved in interactions with host cells, sequestration ofantibodies, invasion into host cells, and with proteins used by phage as receptorsSrt Mediated Secretion: Srt enzymemediates attachmentof specific proteins to the cell surface via aconserved regionon the secreted protein; proteins attached covalently to PGGram-Positive SortaseFor proteins to be secreted by the Sortase enzyme… need 3 motifs to be recognized1.First Motif– specific series of amino acids at the N-terminus of theSignal PeptideProteina.Region is usually cleaved off during passage through the cytoplasmic membrane2.Second Motif– “sorting signal”, series of amino acids (LPXTG) close to the C-terminus of the proteina.This region recognized by the Sortase Enzyme3.Third Motif– series ofpositively charged amino acidsat the C-terminus of the protein6
a.Helps to anchor the protein in the membrane until the Sortase Enzyme is finishedGram-Positive Sortase-Mediated SecretionProcess of sortase-mediated secretion in Gram +1.Signal peptide of sortase substratedirects it to secretory machineryto move it into the periplasm;positively charged C-terminus (3rdmotif) anchors to membrane2.Sortase enzymerecognizes LPXTG motif(2ndmotif)3.Sortasecleavesthe protein substrate4.Sortase transfers protein substrate to a lipid intermediate using peptide cross component of thepeptidoglycan5.Protein/lipid/pentapeptide complex isincorporated into the peptidoglycana.When building a pilus, multiple sortases function to attach pilin subunits together outwardsfrom cell surfaceBacterial ToxinsBacteria can induce disease using toxins by 2 mains ways:ExotoxinsandEndotoxinsBacterial Secretion of ExotoxinsExotoxins must be transported across 2 membranes in Gram-negative bacteriaType 1 Secretion SystemExotoxin is secreted through theformation of a complexbetween the inner membrane ABC and MFPwith the outer membrane trimeric OMPThese proteins form a channelthat the toxin is secreted in a single stepHaemolysin, Exotoxin secreted by Type 1 MechanismHaemolysin: exotoxin secreted by some streptococci, capable of lysing red blood cells (RBC)In real lifered blood agar plates with orange bacteria, yellow zones of clearing indicate hemolysis of RBCsMechanism7

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Term
Fall
Professor
Nancy Martin

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