Membrane bacterial, lipids

Figure 2 Mode of action of the prototypical lantibiotic nisin. (a) The peptidoglycan precursor lipid II is composed of an N-acetylglucosamine-p-1,4-N-acetylmuramic acid disaccharide (GIcNAc-MurNAc) that is attached to a membrane anchor of 11 isoprene units via a pyrophosphate moiety. A pentapeptide is linked to the muramic acid. Transglycosylase and transpeptidase enzymes polymerize multiple lipid II molecules and crosslink their pentapeptide groups, respectively, to generate the peptidoglycan. (b) The NMR solution structure of the 1 1 complex of nisin and a lipid II derivative in DMSO (6). (c) The amino-terminus of nisin binds the pyrophosphate of lipid II, whereas the carboxy-terminus inserts into the bacterial membrane. Four lipid II and eight nisin molecules compose a stable pore, although the arrangement of the molecules within each pore is unknown (5).

Cyclopropane fatty acids occur frequently in bacterial membrane phospholipids. Also, they generally accompany the cyclopropene acids in seed oils (see following paragraph). Though other chain lengths have been reported, the most common cyclopropane acids are Cu and C19 (lactobacillic acid) compounds. They are probably formed from appropriate olefinic acids (16 1 9c and 18 111c) which are widely distributed in bacterial lipids. The cyclopropane acids have cis configuration but it is not clear whether they are individual enantiomers or racemic mixtures. 

On the other hand, glycerophospholipids are usually the major constituents of bacterial membranes. These lipids are usually enriched with saturated fatty acids at the sn-l position and with unsaturated acids at the sn-2 position. In cyanobacteria, the distribution is governed by chain length rather than unsaturation with sn-l-Cis and sn-2-Cte being the rule (Zepke et al., 1978). The cyanobacteria are also exceptional in that they synthesize (and accumulate) only one phospholipid, phosphatidylglycerol. 

Staining Applications Vacuolar membrane plasma membrane bacterial membrane " lipid membrane plasma membrane-bound flav(mroteins nuclear envelope (NE) synaptic vesicles secretory vesicles lac-totroph vesicles synaptic terminals neurons " en-docytosis exocjrtosis smooth-muscle-associated airway receptors (SMARs) in lungs embryos ... 

The fact that the major component of bacterial lipids, the phospho-hpids, is localized in the cell envelope supports the idea of lipids as primary structural components of the cell. The major function of the cell envelope or, more specifically, the cell membrane, is to control the internal environment of the organism. The possibility that lipids are directly involved in active transport has stimulated much work in this field, although at present there is no conclusive evidence to support this idea. The general question of membranes and transport is beyond the scope of diis chapter however, it is worthwhile to consider briefly two studies bearing on the question of lipids in active transport in E. coU. 

First, a short account needs to be given of the main membrane acyl lipids and the composition of the different surface layers. As a generalization, plant (and algal) membranes can be divided into two types with regard to their lipid composition. Most membranes contain the phosphogly-ceride/protein matrix so familiar to biochemists dealing with animal or bacterial systems. In startling contrast, the photosynthetic thylakoid... 

The best-studied example from Class I lantibiotics is nisin (TC l.C.20.1.1). Nisin apparently forms channels in bacterial membranes using Lipid II, the prenyl chain-linked donor of the peptidoglycan building block, both as a receptor and as an intrinsic component of the pore (Breukink... 

Comparison of the amino acid sequences of the L and M subunits of the reaction centers from three different bacterial species shows that about 50% of all residues in those two subunits are conserved in all three species. In the transmembrane helices, sequence conservation varies. Residues that are buried and have contacts either with pigments or with other transmembrane helices are about 60% conserved. In contrast, residues that are fully exposed to the membrane lipids are only 16% conserved. Clearly, fewer restrictions... 

Lipids also undergo rapid lateral motion in membranes. A typical phospholipid can diffuse laterally in a membrane at a linear rate of several microns per second. At that rate, a phospholipid could travel from one end of a bacterial ceil to the other in less than a second or traverse a typical animal ceil in a few minutes. On the other hand, transverse movement of lipids (or proteins) from one face of the bilayer to the other is much slower (and much less likely). For example, it can take as long as several days for half the phospholipids in a bilayer vesicle to flip from one side of the bilayer to the other. 

Kaprelyants, A., Suleimenov, M., Sorokina, A., Deborin, G., El-Registan, G., Stoyanovich, F., Lille, Yu., Ostrovsky, D. Structural-functional changes in bacterial and model membranes induced by phenolic lipids. Biological membranes, Vol.4, No.3, (March 1987), pp. 254-261, ISSN 0748-8653... 

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.)... 

Tamplin et. al. (54) observed that V. cholerae and A. hydrophila cell extracts contained substances with TTX-like biological activity in tissue culture assay, counteracting the lethal effect of veratridine on ouabain-treated mouse neuroblastoma cells. Concentrations of TTX-like activity ranged from 5 to 100 ng/L of culture when compared to standard TTX. The same bacterial extracts also displaced radiolabelled STX from rat brain membrane sodium channel receptors and inhibited the compound action potential of frog sciatic nerve. However, the same extracts did not show TTX-like blocking events of sodium current when applied to rat sarcolemmal sodium channels in planar lipid bilayers. 

Nichols DS, MR Miller, NW Davies, A Goodchild, M Raferty, R Caviccholi (2004) Cold adaptation in the Antarctic arch eon Methanococcoides burtonii involves membrane lipid unsaturation. J Bacterial 186 8508-8515. 

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