Gram-negative bacteria cytoplasmic membrane

Figure 3.2 Representation of the Envelope of Gram-negative Bacteria (cytoplasmic membrane not drawn to scale)...

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... 

AGAC-modifying enzymes are active outside the cytoplasmic membrane, in the periplasmic space in Gram-negative bacteria and extracellularly in Gram-positives. Table 9.4 summarizes some of the enzymes involved in AGAC resistance and their spectrum of activity. 

E. coli, like other Gram-negative bacteria, has an outer membrane which hampers excretion of proteins to the culture media. Thus, expressed proteins can remain in the cytoplasm or can be directed into the periplasm employing the N-terminus fusion of a signal peptide (e.g. OmpA, pelB, OmpF, PhoA, Tat signal peptides) [30]. 

Specific receptors for siderophores and vitamin B12 have been identified in the OM of Gram-negative bacteria. The translocation of these ligands across the outer membrane follows an energy-dependent mechanism and also involves the TonB, ExbB, ExbD proteins anchored in the cytoplasmic membrane. Biochemical and genetic data indicate that these proteins form a functional unit (the Ton complex), which couples the outer membrane receptor-mediated... 

Figure 10. Schematic view of the uptake of ferric siderophores by Gram-positive and Gram-negative bacteria. Please note that the murein (peptidoglycan) network associated with the cytoplasmic membrane is not shown. For details see text...

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 ... 

Gram-negative bacteria have a more complex cell surface. The peptidoglycan layer is also the outer layer with respect to the cytoplasmic membrane. However, besides this, they have another outer polysaccharide membrane. This outer membrane is built out of lipopolysac-charides and lipoproteins, and can be a serious barrier for permeating hydrophilic molecules. 

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.)...

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