Gram-negative bacteria inner membrane

Gram-negative bacteria are surrounded by two membranes, an inner plasma membrane and an outer membrane. These are separated by a periplasmic space. Most plasma membrane proteins contain long, continuous sequences of about 20 hydrophobic residues that are typical of transmembrane a helices such as those found in bacteriorhodopsin. In contrast, most outer membrane proteins do not show such sequence patterns. 

In Gram-negative bacteria the cell wall is only about 3 nm thick, and located in the extended periplasmatic space between the inner membrane (IM) and an additional outer membrane (OM). The lipid monolayer in the outer leaflet of the OM contains about 90% lipopolysaccharides (LPS). LPS consist of Lipid A and an oligosaccharide component, which is highly specific for individual bacterial species and phenotypes [108, 114]. 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

Many bacteria secrete a wide range of proteins including pathogenic factors such as toxins. They must pass through both the outer and inner membranes. There are various mechanisms for protein secretion. Among them, three pathways are conserved in many species of gram-negative bacteria (Salmond and Reeves, 1993 Nunn, 1999). 

ESR spectra indicated that ultrasound enhanced the penetration of 16-DS into the structurally stronger sites of the inner and outer cell membranes. The effect of ultrasound on the cell membranes was transient in that the initial membrane permeability was restored upon termination of the ultrasound treatment. These results suggested that the resistance of gram-negative bacteria to the action of hydrophobic antibiotics was caused by a low permeability of the outer cell membranes and that this resistance may be reduced by the simultaneous application of antibiotic and ultrasound. 

The insertion of (i-barrel precursors is one of the two translocation processes, besides the sorting of inner membrane and IMS proteins, that are clearly derived from a eubacterial translocation system. (1-Barrel proteins are exclusively found in the outer membranes of Gram-negative bacteria and of endosymbiotic organelles such as mitochondria and plastids (Wim-... 

The outer membranes of mitochondria can be removed from the inner membranes by osmotic rupture.13 Analyses on separated membrane fractions show that the outer membrane is less dense (density — 1.1 g / cm3) than the inner (density 1.2 g / cm3). It is highly permeable to most substances of molecular mass 10 kDa or less because of the presence of pores of 2 nm diameter. These are formed by mitochondrial porins,14-17 which are similar to the outer membrane porins of gram-negative bacteria (Fig. 8-20). The ratio of phospholipid to protein ( 0.82 on a weight basis) is much higher than in the inner membrane. Extraction of the phospholipids by acetone destroys the membrane. Of the lipids present, there is a low content of cardiolipin, a high content of phosphatidylinositol and cholesterol, and no ubiquinone. 

Mitochondria, Gram negative bacteria, and chloroplasts have double envelopes of membranes. As we discussed, their inner membranes are impermeable to ions and polar molecules other than those that are transported by specific... 

Artificial asymmetric membranes composed of outer membranes of various species of Gram-negative bacteria and an inner leaflet of various phospholipids have been prepared using the Montal-Mueller technique [65]. Such planar bilayers have been used, for example, to study the molecular mechanism of polymyxin B-mem-brane interactions. A direct correlation between surface charge density and self-promoted transport has been found [66]. 

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...

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