Lipoproteins, Membranes

After uptake, lipophilic pollutants tend to move into hydrophobic domains within animals or plants (membranes, lipoproteins, depot fat, etc.), unless they are biotransformed into more polar and water soluble with compounds having low Metabolism of lipophilic compounds proceeds in two stages ... 

Pectin methylesterase B of Erwinia chrysanthemi, the first pectinase characterise(l as a membrane lipoprotein. 

Matsuyama, S., Yokota, N., and Tokuda, H. (1997). A novel outer membrane lipoprotein, LolB (HemM) involved in the LolA (p20)-dependent localization of lipoproteins to the outer membrane of Escherichia coli. EMBO J. 16, 6947-6955. 

Interference with cell-wall synthesis Interference with cell division Inhibition of neuromuscular transmission Interference with protein synthesis Depletion of membrane lipoproteins... 

Isolation. Numerous methods have been developed for the purification of XO from milk since the enzyme is concentrated in the MFGM, in which it is one of the principal proteins, all methods employ cream as starting material, use a dissociating agent to liberate XO from membrane lipoproteins and some form of chromatography for further purification. 

We have been interested in the contribution made by plasma GSL towards cell membrane-lipoprotein interaction with regard to ... 

The mechanism of propagation is very effective as a defense mechanism when it is oriented toward bacteria or virus membranes, but it may be very inappropriate once it is directed against the host membranes (lipoproteins, endothelial cells, internal membranes, etc.). 

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... 

A similar type of interaction is thought to occur in membrane lipoprotein molecules. The problem in the latter studies is that the membrane apoproteins are not easily solubilized. If further information on the structure of biological membranes is required, then it is recommended that a recent book by Petty (1993) and one edited by Wirtz et al. (1993) be placed on a must reading list. An older, but very good, short review on lipid-protein interaction possibilities in membranes is one presented by Danielli (1982), who is widely recognized as a pioneer as well as a legend in this field. 

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. 

Surprisingly, E. coli mutants completely lacking either PE and PS or PG and CL are viable. Null mutants in the pgsA gene (encodes PG phosphate synthase) that cannot synthesize PG and CL are lethal, but suppressors of this mutation have been identified [11]. In such mutants, the major outer membrane lipoprotein precursor (Fig. 4), which depends on PG for its lipid modification, accumulates in the inner membrane and apparently kills the cell. Cells unable to make this lipoprotein are viable but are temperature sensitive for growth at 42°C indicating that PG and CL are not absolutely required for viability, only for optimal growth. However, the anionic nature of these lipids (apparently substituted by increased levels of PA) is necessary for the proper membrane association and function of peripheral membrane proteins, as discussed in Sections 5.2.5 and 5.5.2. 

Fig. 9. Phospholipid turnover. The 1,2-diacylglyceroI kinase cycle involves the (1) transfer of the sn-1 -glycerol phosphate moiety from phosphatidylglycerol to MDO by the enzyme MdoB. (2) Diacylglycerol kinase converts the diacylglycerol to phosphatidic acid, which can regenerate the phosphatidylglycerol (see Fig. 6). Phosphatidylethanolamine cycling involves (3) the transfer of an acyl chain to membrane lipoprotein and (4) re-esterification of the 1-position by 2-acylgiycerophosphoethanolamine (Aas).

In addition to subunits L, M, and H, the RCs of several purple bacteria such as Rp. viridis, Rhodocydus (Rc.) gelatinosus, and Chromatium vinosum contain a tightly bound tetraheme cyto-chrome-c subunit which donates electrons to D. In Rp. viridis, this subunit does not possess intramem-branous segments, but it has an N-terminal cysteine that is linked to a glycerol residue via a thioether bond (Weyer etal., 1987). Such a bond has also been found at the N-terminus of the major outer membrane lipoprotein of Escherichia coli (Hantke and Braun, 1973) in which the fatty acids form a lipid-type membrane anchor. 

Sonntag, I., Schwartz, H., Hirota, Y. and Henning, U., 1978, Cell envelope and shape of Escherichia coli multiple mutants missing the outer membrane lipoprotein and other major outer membrane proteins. J. Bacteriol. 136 280-285. 

Several studies have shown that PMN production of cytokines during microbial stimulation requires activation of MAPK. Using specific MAPK inhibitors, neutrophil IL-8 production in response to LPS, Mycoplasma fermentans membrane lipoproteins, type III group B streptococci, as well as TNF-a and GM-CSF was found to be dependent upon p38 MAPK [22-24,33]. The ERKl/2 and p38 MAPK are also involved in LPS andM. fermentans membrane lipoprotein-stimulated IL-8 production, as determined by inhibitor studies with PD98059 and SB203580 [22]. 

Marie C, Roman-Roman S, Rawadi G Involvement of mitogen activated protein kinase pathways in interleukin-8 production by human monocytes and polymorphonuclear cells stimulated with lipopolysaccharide or Mycoplasma fermentens membrane lipoproteins. Infect Immun 1999 67 688-693. 

Despite the low lipid content in seaweed, the presence of vitamin E is relevant as it acts as a strong antioxidant which prevents the formation of free radicals. a-Tocopherol, the most important member of tocol group, is capable of fixing free radicals via its phenol group in the structure and thus is considered to play an important role in oxidation of biological membranes, lipoproteins, and fat deposits, controlling or reducing lipid peroxidation (Sanchez-Machado et al, 2002). 

Cholesterol A lipid substance that we both make and take in via our diet. Important component of membranes, lipoproteins, etc. but in excessive levels contributes to atherosclerotic plaques. Precursor of steroid hormones. 

Nemerson, Y., Esnouf, M.P. Activation of a proteolytic system by a membrane lipoprotein Mechanism of action of tissue factor. Proc. nat. Acad. Sci. (Wash.) 70, 310 -314 (1973)... 

---