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

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

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

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

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

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

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

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

reading Saier, M.H. Jr. 2003. Tracing pathways of transport evolution. Mol. Microbiol. 48:1145-1156 health.library.mcgill.ca/ejournal/fulltxt.htm M

Quiz #1: 17.09.03 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]

Quiz #1:Porins Found in G -, not in G+ May be > 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 β strands, 8 surface-exposed loops Synthesized as precursor  mature species