Cytoplasmic membrane, bacterial channels

In their natural environment, bacterial cells need to adapt to a wide range of osmotic conditions. Escherichia coli cells exposed to hypo-osmotic shock respond by a rapid release of cellular osmolytes such as proline, potassium glutamate, trehalose, and ATP. This ability prevents the cells from lysis by decreasing the turgor pressure on the challenge of a sudden shift in osmolarity. Bacterial MS channels, MscL and MscS (Fig. la and b), are major components of adaptation mechanisms to hypo-osmotic shock. Being located in the cytoplasmic membrane, MscL and MscS are activated by an increase of membrane tension... 

Figure 1 Examples of several bacterial membrane proteins. The outer membrane (OM) of Gram-negative bacteria contains exclusively fS-barrel proteins, and three examples are shown BtuB (PDB ID 1NQF), which is the 22 p-stranded TonB-dependent active transporter for vitamin B 2/ th LamB or maltoporin trimer (PDB ID 1AF6), which is the 18 p-stranded passive sugar transporter and OmpA (PDB ID 1BXW), which is an 8 p-stranded protein that provides structural support for the OM. Proteins in the cytoplasmic membrane (CM) are helical, and three examples are shown the potassium channel KcsA (PDB ID 1BL8), which is a tetramer Sec YEG (PDB ID 1RH5), which forms the protein transport channel in Methanococcus and BtuCD (PDB ID ...

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. 

The detailed mechanism of action of cationic peptides is described in Section IVC. The most prominent effect on cells is the formation of channels m or disruptions of the cytoplasmic membrane. Thus, these molecules appear to kill by a physical method that takes advantage of the specific composition of bacterial membranes. In contrast, most... 

As discussed above, cationic peptides can form channels in model bilayers. Thus, it seems likely that their primary amibacterial action is to disrupt the integrity of bacterial cytoplasmic membranes. This would have the effect of permitting leakage of ions arxl small metabolites, and destroying the ability of bacteria to maintain a transmembrane proton gradient (proton-motive force) with consequent loss of ability to generate adenosine triphosphate and transport substrates (see Ref. 119 for review of cytoplasmic membranes). 

The important bacterial storage material poly-hydroxybutyric acid is related metabolically and structurally to the lipids. This highly reduced polymer is made up of D-(3-hydroxybutyric acid units in ester linkage, about 1500 residues being present per chain. The structure is that of a compact right-handed coil with a twofold screw axis and a pitch of 0.60 nm.a Within bacteria it often occurs in thin lamellae 5.0 nm thick. Since a chain of 1500 residues stretches to 440 nm, there must be 88 folds in a single chain. Present in both cytoplasmic granules and in membranes,b polyhydroxybutyrate can account for as much as 50% of the total carbon of some bacterial In E. coli and many other bacteria polyhydroxybutyrate is present in a lower molecular mass form bound to calcium polyphosphates, proteins, or other macromolecules.d e It has also been extracted from bovine serum albumin and may be ubiquitous in both eukaryotes and prokaryotes.d/e The polymer may function in formation of Ca2+ channels in membranes.b/d... 

Galvez, A., Maqueda, M., Martinez-Bueno, M., and Valdivia, E. (1991). Permeation of bacterial cells, permeation of cytoplasmic and artificial membrane vesicles, and channel formation on lipid bilayers by peptide antibiotic AS-48. J Bacteriol 173, 886-892. 

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