Gram-negative bacteria transport across

Currently, five different molecular classes of mdr efflux pumps are known [5], While pumps of the the ATP-binding cassette (ABC) transporter superfamily are driven by ATP hydrolysis, the other four superfamilies called resistance-nodulation-division (RND), major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), and small multidrag resistance transporter (SMR) are driven by the proton-motive force across the cytoplasmic membrane. Usually a single pump protein is located within the cytoplasmic membrane. However, the RND-type pumps which are restricted to Gram-negative bacteria consist of two additional components, a periplasmic membrane fusion protein (MFP) which connects the efflux pump to an outer... 

TRANSPORT ACROSS THE OUTER MEMBRANE OF GRAM-NEGATIVE BACTERIA... 

The uptake of siderophore-iron complexes by Gram-negative bacteria is energy dependent and occurs via specific outer membrane proteins. In the periplasmic space, it binds to its cognate periplasmic binding protein and is then actively transported across the cytoplasmic membrane by an ATP-trans-porter protein. Three principal mechanisms for transport through the outer membrane have been described ... 

The lipid membranes are a few nanometers thick. They contain proteins whose role is to actively transport particular target chemicals across these nonpolar barriers. The outer membranes of gram negative bacteria also have protein channels called porins that allow passage of small polar and charged substrates. 

Fig. 4.12 Mechanism proposed for the transport of antimicrobial peptides across the outer membrane of Gram-negative bacteria. The initial recognition involves the negatively charged LPS on the outer leaflet and the cationic peptide. Once in the periplasmic space, the peptide can move into the cytoplasmic membrane. (Reprinted from Fig. 6 of ref. 113 with permission from Elsevier Science.)...

Figure 2 Siderophore-mediated iron-uptake systems in E. coli. Siderophore-iron complexes bind to transporter proteins located in the outer membrane (also known as OM), a barrier that is characteristic of Gram-negative bacteria. The region between the outer and inner is known as the periplasmic space. Specific carrier proteins such as FhuD transport iron fi om the outer membrane to the inner or cytosolic membrane (also known as CM). The TonB/ExbB/ExbD complex spans the inner and outer membranes and interacts with FepA, as shown, as well as all of the outer membrane receptors. The linkage that the TonB/ExbB/ExbD complex provides between the inner or cytosolic membrane to the outer membrane is thought to allow transmission of sufficient energy from the cytosol to drive siderophore-iron uptake across the outer membrane...

MECHANISM OF ACTION AND RESISTANCE Tetracyclines inhibit bacterial protein synthesis by binding to the 30S bacterial ribosome and preventing access of aminoacyl tRNAto the acceptor (A) site on the mRNA-ribosome complex (Figure 46-1). They enter gram-negative bacteria by passive diffusion through channels formed by porins in the onter ceU membrane and by active transport that pumps tetracyclines across the cytoplasmic membrane. 

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