Bacterial membranes structure

Disruption of bacterial membrane structure Polymyxins Colistin Altered target Efflux... 

Polymyxins (bactericidal disrupt bacterial membrane structural integrity)... 

Roszkowski K, Roszkowski W, Ko HL, Szmigielski S, Pulverer G and Jeljaszewicz J (1982) Clinical e q)erience in treatment of cancer by propionibacteiia. In Jeljaszewicz J, Pulverer G and Roszkowski W (eds) Bacteria and Cancer, pp 331-357. Academic Press, London Roszkowski W, Roszkowski K, Ko HL, Beuth J and Jeljaszewicz J (1990) Immunomodulation by propionibacteria. Zbl Bakt Hyg 274 289-298 Saino Y, Eda J, Nagoya T, Yoshimura Y, Yamaguchi M and Kobayashi F (1976) Anaerobic coryneforms isolated from human bone marrow and skin. Jap J Microbiol 20 17-25 Salton MRJ and Owen P (1976) Bacterial membrane structure. Annu Rev Microbiol 30 451-482... 

The three-dimensional structure of the bacterial membrane protein, bac-teriorhodopsin, was the first to be obtained from electron microscopy of two-dimensional crystals. This method is now being successfully applied to several other membrane-bound proteins. 

Enveloped viruses Many viruses have complex membranous structures surrounding the nucleocapsid. Enveloped viruses are common in the animal world (for example, influenza virus), but some enveloped bacterial viruses are also known. The virus envelope consists of a lipid bilayer with proteins, usually glycoproteins, embedded in it. Although the glycoproteins of the virus membrane are encoded by the virus, the lipids are derived from the membranes of the host cell. The symmetry of enveloped viruses is expressed not in terms of the virion as a whole but in terms of the nucleocapsid present inside the virus membrane. 

Koronakis, V., Sharff, A., Koronakis, E., Luisi, B. and Hughes, C. (2000). Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export, Nature, 405, 914—919. 

Buchanan, S. K. (1999). Beta-barrel proteins from bacterial outer membranes structure, function and refolding, Curr. Opin. Struct. Biol., 9, 455-461. 

The initial adherence of pathogens to host cell surfaces is considered an essential step in colonization and infection (Savage, 1977, 1984). Therefore, identifying the bacterial molecules that mediate adherence has been a major area of research, especially since these molecules may serve as targets for anfi-adherence strategies. As discussed previously (Section VI), the detailed interactions between a pathogen and a host cell are often mediated by proteinaceous surface structures on the bacterial surface. These bacterial proteins are referred to as adhesins (Finlay and Falkow, 1989), and are most often foimd on the tips of bacterial fimbriae or pili (fimbrial adhesins), but may also be anchored in the bacterial membrane so that it can be presented on the bacterial outer membrane (afimbrial adhesins) (Sharon and Ofek, 1986). Models of fimbrial and afimbrial adhesins of some human pathogens are discussed here. 

The late factors C5 to C9 are responsible for the development of the membrane attack complex (bottom). They create an ion-permeable pore in the bacterial membrane, which leads to lysis of the pathogen. This reaction is triggered by C5 convertase [2]. Depending on the type of complement activation, this enzyme has the structure C4b2o3b or C3bBb3b, and it cleaves C5 into C5a and C5b. The complex of C5b and C6 allows deposition of C7 in the bacterial membrane. C8 and numerous C9 molecules—which form the actual pore—then bind to this core. 

In the search for structural diversity, and novel therapeutic agents, unique ring structures like the 1,2,5-thiadiazole have always captured the imagination of chemists. Often, as in the case of timolol (4), the interest is rewarded. In the early 1990s, a simple thiadiazole was appended to a penem in the development of the structure-activity relationships for a series of ) -lactamase inhibitors. The result was enhanced penetration of the bacterial membrane and a broader spectrum of activity versus clavulanic acid <9lJAN33l>. 

Fig. 5.3. Structure of the OmpF porin of E. coli. The porin is a bacterial membrane protein with P-sheet structures as transmembrane elements. The structure of a monomer of the OmpF porin is shown. In total, 16 P-bands are configured in the form of a cylinder and form the waUs of a pore through which selective passage of ions takes place. LI—L8 are long loops, Tl,2,3 and T7,8 are short bends (T turn) that fink the P-sheets. According to Cowan et al. (1992), with per-...

It serves to control the passage of small molecules into and out of the cell. Its outer surface carries receptors for recognition of various materials. The inside surface of bacterial membranes contains enzymes that catalyze most of the oxidative metabolism of the cells. Bacterial cell membranes are sometimes folded inward to form internal structures involved in photosynthesis or other specialized reactions of metabolism such as oxidation of ammonia to nitrate.2 In E. coli replication of DNA seems to occur on certain parts of the membrane surface, probably under the control of membrane-bound enzymes. The formation of the new membrane which... 

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). 

Many cytochromes c are soluble but others are bound to membranes or to other proteins. A well-studied tetraheme protein binds to the reaction centers of many purple and green bacteria and transfers electrons to those photosynthetic centers.118 120 Cytochrome c2 plays a similar role in Rhodobacter, forming a complex of known three-dimensional structure.121 Additional cytochromes participate in both cyclic and noncyclic electron transport in photosynthetic bacteria and algae (see Chapter 23).120,122 124 Some bacterial membranes as well as those of mitochondria contain a cytochrome bct complex whose structure is shown in Fig. 18-8.125,126... 

In green plants, which contain little or no cholesterol, cydoartenol is the key intermediate in sterol biosynthesis.161-1623 As indicated in Fig. 22-6, step c, cydoartenol can be formed if the proton at C-9 is shifted (as a hydride ion) to displace the methyl group from C-8. A proton is lost from the adjacent methyl group to close the cyclopropane ring. There are still other ways in which squalene is cyclized,162/163/1633 including some that incorporate nitrogen atoms and form alkaloids.1631 One pathway leads to the hop-anoids. These triterpene derivatives function in bacterial membranes, probably much as cholesterol does in our membranes. The three-dimensional structure of a bacterial hopene synthase is known.164 1643 Like glucoamylase (Fig. 2-29) and farnesyl transferase, the enzyme has an (a,a)6-barrel structure in one domain and a somewhat similar barrel in a second domain. 

Principles to stabilize lipid bilayers by polymerization have been outlined schematically in Fig. 4a-d. Mother Nature — unfamiliar with the radically initiated polymerization of unsaturated compounds — uses other methods to-stabilize biomembranes. Polypeptides and polysaccharide derivatives act as a type of net which supports the biomembrane. Typical examples are spectrin, located at the inner surface of the erythrocyte membrane, clathrin, which is the major constituent of the coat structure in coated vesicles, and murein (peptidoglycan) a macromolecule coating the bacterial membrane as a component of the cell wall. Is it possible to mimic Nature and stabilize synthetic lipid bilayers by coating the liposome with a polymeric network without any covalent linkage between the vesicle and the polymer One can imagine different ways for the coating of liposomes with a polymer. This is illustrated below in Fig. 53. 

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