Bacterial transport mechanisms

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Bacterial transport mechanisms

• Lengeler et al.
• Chapter 5, p. 68-87
• Multiple roles of procaryotic cell membranes
• Growth
• Three kinds of transporters
• Molecular mechanisms

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Transport systems

• Bacteria usually starved
• Transport S medium ? inside cell
• Growth curves
• Inoc into fresh medium lag ? log
• Exhaust one nutrient stationary

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Transport

• Mechanism to obtain nutrients and.
• to maintain optimal intracellular of
  intermediates
• Location of transporters
• OM barrier porins small transporters
• Periplasm p/g not a diffusion barrier
• CM true osmotic barrier

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Transport systems

• Simple diffusion
• O2 CO2 NH3
• Non polar cmpds antibiotics
• No specific carriers
• Facilitated diffusion
• Process of passage through a membrane by an
  impenetrable cmpd
• Requires a carrier

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• Facilitated diffusion
• S on outside high
• S on inside low
• GlpF of E. coli
• Glycerol facilitator
• Aquaporin

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• Active transport
• Concentration gradient
• E. coli amino acids, 103 x
• galactose, 105 x
• K, 106 x
• Permeases
• Membrane-embedded proteins
• Stereospecific
• Saturation kinetics

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Active transport proteins

• 2 subsets
• Major facilitator superfamily (MFS)
• Transduces free energy stored in electrochemical
  proton gradient.
• ?substrate concentration gradients
• P-type ATPases ABC transporters
• Energy from ATP hydrolysis.
• Drives solute accumulation

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Transport proteins

• Examples
• MFS
• galactosides_LacY of E. coli
• ABC transporters
• maltose_multicomponents (Mal proteins) of E. coli
• Relevance
• Depression, stroke, diabetes, multidrug
  resistance
• Prozac, Prilosec membrane proteins
• 3o structure, mechanisms conserved

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reading

• Saier, M.H. Jr. 2003. Tracing pathways of
  transport evolution. Mol. Microbiol. 481145-1156
  
• health.library.mcgill.ca/ejournal/fulltxt.htm
• M

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Quiz 1 17.09.03

1. Porins are pore-forming proteins at the surface
   of Gram-negative bacteria. Write eight
   (grammatically complete) sentences, each sentence
   describing a distinguishing feature or
   characteristic of bacterial porins. 8 points
2. Inside a Living Cell three coloured diagrams 2
   points

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Quiz 1Porins

• Found in G -, not in G
• May be gt 1 species of porin for some bacteria
• E. coli OmpF, OmpC
• Mr 35-40 kDa
• Organized as trimers, self assemble
• Form water-filled channels,
• passive diffusion pores across OM
• Reconstuituted into LPS/P-lipid vesicles
• Different Mr exclusion limits
• Structural features constriction zone
• Crystal structures
• 16 anti-parallel ß strands, 8 surface-exposed
  loops
• Synthesized as precursor ? mature species