Bacterial membranes composition

Bacterial membranes have a much more complex construction than mammalian membranes. This enables bacteria to survive in the various environments of host organisms. Knowledge of the composition and functioning of bacterial membranes is therefore essential to the development of anti-infective drugs. In order to be effective, antibacterial agents not only have to have optimal pharmacokinetic properties such as uptake and distribution in the patient, but they must also be able to cross an additional barrier, the cell wall of the bacteria, so that they can reach the target site. This additional barrier is remarkable on account of its rigidity and permeability. The construction and structural uniqueness of this barrier is briefly described below. 

Solid supported bilayers of other composition have also been reported such as lipopolysaccharide bilayers which can mimic the outer bacterial membrane with this example used to monitor bacteriophage interaction by AFM [81]. 

According to Ovchinnikov and coworkers, the antibiotic activity of valinomycin is due to impairment of alkali ion transport in bacterial membranes217 The main arguments for this theory are (i) None of the synthetic non-complexing analogs has antibiotic activity (ii) enantio-valinomycin has the same antibiotic activity as valinomycin, thus excluding interaction with a stereospecific receptor (iii) valinomycin increases the cation permeability of bacterial membranes (iv) the antimicrobial action of valinomycin depends on the cation composition of the medium. 

The sensitivity of supramolecular assemblies such as microtubuli and flagellin suggests that we may expect that cells are quite sensitive to pressure. Without much hesitation we may consider the cell as a molecular factory. This is supported by the observations on viruses. Very small pressures induce changes that make viruses biologically inactive although the structure may be little affected. The molecular adaptation mechanisms that play a role in the composition of bacterial membranes may be interpreted along the same lines. 

The polymer efficiently permeabilises anionic vesicles with compositions which mimic those of bacterial membranes. The polymer binds to anionic phospholipid vesicles but not zwitterionic vesicles, which causes phase separation in anionic phospholipid mixtures, clustering the negative charge. The polymer permeabilises the outer membrane of Escherichia coli ML-35p in a biphasic manner low polymer concentrations permeabilise the inner membrane of Escherichia coli ML-35p, whereas high concentrations of the polymer can block the active transport of or onitrophenyl-P-n-galactoside in wild-type Escherichia coli K12 [17]. 

In view of the fact that leaf lipids are dominated by those of the chloroplasts, it is worth emphasizing certain features of the latter s membranes. In contrast to mammalian and most bacterial membranes phospholipids are minor components. Phos-phatidylglycerol is the only phosphoglyceride of importance. About 75% of the acyl lipid content is glycosylglyceride (Table 3.215). In addition, the fatty acid composition of chloroplast acyl lipids is unusually rich in polyunsaturates. a-Linolenic acid, the main fatty acid, is particularly enriched in the two galactosylglycerides. Phosphatidylglycerol also con-... 

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... 

The process of insertion causes changes in phase and/or motion of the tipids of the target membrane (112). However, the lipid composition can dramatically influence the possibility of insertion, and positively charged phospholipids and cholesterol decreased the formation of membrane channels by cecropin by 5- to 60 fold (36). Indeed, this may explain, in addition to the difference in the selectivity of cationic antibacterial pep tides for bacteria over eukaryotes, since the former lack cholesterol, which is abundant in eukaryotic membranes, whereas anionic phosphatidyl glycerol and cardiodipin. major components of bacterial membranes, represent excellent target lipids. 

The phospholipid composition also is an important taxonomic indicator of the genus. Biochemical activity of the cell depends considerably on the association of some specific proteins with phospholipids. In bacterial membranes one major phospholipid, accounting for 50% or more of the total, is usually found (Salton and Owen, 1976). The major phospholipid class in propionibacteria is represented by glycolipids, which amount to about 40% of the total lipids in P. shermanii, with smaller amounts in P. freudenreichii and P. arabinosum (Shaw and Baddiley, 1968). The exact... 

C. Bodhibukkana, S.T. Kaewnopparat, N. Tangthong, P. Bouking, G.P.R. Martin, Suedee bacterially-derived composite membranes of cellulose cuid molecularly imprinted polymer for use as a transdermal enantioselective controlled-release system of racemic propranolol, /. Controlled Release, 113,43-56,2006. 

The lipid composition of membranes is a sensitive indicator of changes in environmental temperature. The fluidity of a membrane is critical to its functioning as a semi-permeable barrier, and is directly related to the fatty acid composition of the membrane. In artificial lipid membrane the liquid to crystalline transition occurs at lower temperatures for phospholipids containing higher proportions of shorter chain fatty acids or increased degree of unsaturation. Bacterial membranes with a greater proportion of unsaturated fatty acids are better able to function at low temperatures. 

Membrane Composition. Biological membranes consist mostly of protein and lipid in roughly comparable quantities by weight. The overall composition of a variety of different membranes is given in Table 1.1. Values range from the relatively protein-rich inner mitochondrial and bacterial membranes which contain 70-80%... 

FIG. 14 Schematic illustration of an archaeal cell envelope structure (a) composed of the cytoplasmic membrane with associated and integral membrane proteins and an S-layer lattice, integrated into the cytoplasmic membrane, (b) Using this supramolecular construction principle, biomimetic membranes can be generated. The cytoplasmic membrane is replaced by a phospholipid or tetraether hpid monolayer, and bacterial S-layer proteins are crystallized to form a coherent lattice on the lipid film. Subsequently, integral model membrane proteins can be reconstituted in the composite S-layer-supported lipid membrane. (Modified from Ref. 124.)... 

Little is known of how the biosynthetic metabolon is assembled, what mechanisms control the membrane-specific targeting, and how the conversions to apocarotenoids occur. Yet the current approach to drive import of bacterial or plant genes is to use transit sequences of a stromal protein that may limit the effectiveness of the transgene. In addition, for specific applications of controlling carotenoid composition, we need to better understand the interactions of the various enzymes,... 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

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