Bacterial membranes lipoprotein

A lipoprotein present in the periplasmic space of E. coli is anchored to the outer bacterial membrane by a triacylated modified N-terminal cysteine containing a glyceryl group in thioether linkage as shown in the following structure (see also Section E,l). 

The results are shown diagramatically in Figure 5. The left bar shows the analytical breakdown of 100 mg. of exponential cell substance. Protein of the cytoplasm is shown in white and the area corresponding to the protein moiety of the membrane lipoprotein is marked by vertical dashed lines. The sum of these two protein fractions is nearly the same in all three instances. This is to be expected, since the total amount of bacterial protein cannot increase further after one of the protein-essential nutrients has been used up. The left bar shows the calculated composition of an exponentially growing culture at the depletion point, whether the depleted nutrient is valine, threonine, or any other nutrient. The center bar shows the total amount of bacterial... 

Membrane ATPases have also been inhibited by carbodiimides. This reaction is associated with the membrane lipoprotein. Carbodiimide binding proteins have been isolated from bacterial membranes, chloroplasts, animal liver mitochondria, bovine heart mitochondria,molds and yeasts. The site of carbodiimide attack in the protein is probably in the hydrophobic region because only lipophilic carbodiimides are effective inhibitors. The addition of methyl glycinate protects erythrocyte membrane ATPase against carbodiimide inhibition. The inhibition reaction of carbodiimides may involve an O N acyl shift in the initially formed O-acylurea. 

There have been several reports of lipoprotein fractions associated with the microsomal fraction 50, 59) which were rapidly labeled by amino acids in vivo, and which also showed rapid turnover. Such a lipoprotein fraction was also recently reported in bacterial membranes 14S). Amino acids, and possibly peptides, bound to phospholipids have also been reported in Penicillium chrysogenum 370) and in the membranes of L. casei 300). The relation of these compounds to protein synthesis has not been investigated, but their finding does open the interesting possibility that, in analogy with the ribose hydroxyls of RNA, the free hydroxyls of phospholipid glycerol mi t serve to carry activated amino acids. 

Phosphatidylcholine is an integral component of the lipoproteins. On the other hand, it is less often found in bacterial membranes, perhaps 10% of species. It is a neutral or zwitterionic phospholipid over a pH range from strongly acid to strongly alkaline. Because of... 

Up to now, the pectinolytic enzymes of E. chrysanthemi that have been detected were extracellular secreted enzymes (PelA, B, C, D, E, L, exo-Peh and PemA), periplasmic (exo-Pel), or cytoplasmic (OGL) proteins (1, 5). In contrast, PemB is an outer membrane pectinolytic enzyme. To our knowledge it is the first pectinase characterised as a membrane protein. We presented several lines of evidence showing that PemB is a lipoprotein (i) Its N-terminal sequence has the characteristics of lipoprotein signal sequences, (ii) PemB is synthesised as a high molecular weight precursor processed into a lower molecular weight mature form, (iii) Palmitate, the most prevalent fatty acid in bacterial lipoproteins (12), is incorporated into PemB. 

Bacterial lipoproteins are anchored at the membrane by their covalently linked lipid moiety. Although they are first anchored at the inner membrane on their synthesis, some portion of them are then transfered to the outer membrane. Therefore, some sorting machinery must exist. It has been revealed that there is a specific pathway that includes the... 

Phospholipid molecules in the plasma membrane diffuse rapidly enough to go from one end of an average-sized animal cell to the other in a few minutes. In a bacterial cell, such a trip would take only a few seconds. Integral membrane proteins move more slowly than phospholipids, as we expect in view of their greater mass. Diffusion of membrane proteins plays essential roles in many biochemical processes, including the cellular uptake of lipoproteins (chapter 18), responses of cells to hormones (chapter 24), immunological reactions (supplement 3), vision (supplement 2), and the transport of nutrients and ions. As we see in a later section, however, some membrane proteins cannot move about rapidly because they are attached to cytoskeletal scaffolds. 

Gram-positive bacteria contain a rigid peptidoglycan cell wall surrounding the cytoplasmic membrane. Gram-negative bacteria contain an additional third, outer layer. This wall is a complex structure with lipoproteins and lipopolysaccharides. Synthesis of two outer walls from different bacterial cells is described in this concept screen ... 

We selected Pseudomonas pictorum (ATCC 23328) as another model system because it can degrade cholesterol. The standard encapsulation method does not result in a high-porosity membrane that would allow lipoprotein-cholesterol to cross. Therefore, we devised a modified method to prepare high-porosity agar microspheres. There was no evidence of leakage of the enclosed bacteria. Open pore agar beads were incubated in serum, and the bacterial action did not significantly... 

In addition to being found in vertebrates and insects, lipoproteins are also found in bacteria [62]. Bacterial lipoproteins are a set of membrane proteins with distinct functions, such as adhesion to host cells, modulation of inflammatory processes, and translocation of virulence factors into host cells. These properties of bacterial lipoproteins may be utilized for development of strong vaccine adjuvants. 

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