1. Bacterial transport mechanisms
Lengeler et al.
Chapter 5, p
Multiple roles of procaryotic cell membranes
Growth
Three kinds of transporters
Molecular mechanisms

2. Transport systems Bacteria usually starved
Transport S: medium  inside cell
Growth curves:
Inoc into fresh medium; lag  log
Exhaust one nutrient; stationary

3. 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

4. Transport systems Simple diffusion Facilitated 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

5. Facilitated diffusion
[S] on outside = high
[S] on inside = low
GlpF of E. coli
Glycerol facilitator
Aquaporin

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

7. 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

8. Transport proteins Examples Relevance MFS: ABC transporters:
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

9. reading
Saier, M.H. Jr Tracing pathways of transport evolution. Mol. Microbiol. 48:
health.library.mcgill.ca/ejournal/fulltxt.htm M

11. Quiz #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]
Inside a Living Cell: three coloured diagrams [2 points]

12. Quiz #1:Porins Found in G -, not in G+
May be > 1 species of porin for some bacteria
E. coli OmpF, OmpC
Mr 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 β strands, 8 surface-exposed loops
Synthesized as precursor  mature species