Receptors in Bacteria

Hackstein et al ° have suggested that there may be a phylogenetic basis for the occurrence of significant methane formation in the gut of animals. It was argued that this refiected the presence of a methanogen receptor in the gut of animals which support large populations of these bacteria, since the production of... 

CFTR has a single-channel conductance of about 8 pS. It is present in the apical membranes of many epithelia. Its mutation leads to the potentially lethal disease cystic fibrosis. In addition to acting as a chloride channel, CFTR is also thought to regulate, e.g., the epithelial sodium channel ENaC, a molecularly unknown outwardly-rectifying chloride channel, and possibly also potassium channels and water channels. Some of these potential regulatory processes, however, are controversial. CFTR also acts as a receptor for bacteria. 

PUSZTAI A, EWEN S W, GRANT G, PEUMANS W J, VAN DAMME E J, COATES M E, BARDOCZ S (1995) Lectins and also bacteria modify the glycosylation of gut surface receptors in the rat Glycoconj J. 12 22-35. 

In general, virus receptors carry out normal functions in the cell. For example, in bacteria some phage receptors are pili or flagella, others are cell-envelope components, and others are transport binding proteins. The receptor for influenza vims is a glycoprotein found on red blood cells and on cells of the mucous membrane of susceptible animals, whereas the receptor site of poliovirus is a lipoprotein. However, many animal and plant viruses do not have specific attachment sites at all and the vims enters passively as a result of phagocytosis or some other endocytotic process. 

Stallmeyer, B., Schwarz, G., Schulze, J., Nerlich, A., Reiss, J., Kirsch, j., and Mendel, R. R. The neurotransmitter receptor-anchoring protein gephyrin reconstitutes molybdenum cofactor biosynthesis in bacteria, plants, and mammalian cells, Proc Natl Acad Sci USA 1999, 96, 1333-1338. 

Figure 18.4 Effects of cytokines on fate of iron during an infection. Transferrin is the form in which iron is transported in the blood (Chapter 15). Cytokines increase the number of ferritin receptors in proliferating lymphocytes, to facilitate the uptake of iron by lymphocytes. They also stimulate synthesis of apofer-ritin in the liver, which removes iron from the blood to reduce that available for bacteria. (See Chapter 15 for discussion of iron metabolism)...

This herb has been part of folk medicine since pre-Christian times (247). It has been primarily used as a sedative and for the treatment of epilepsy. Consistent with this use, this herb reportedly can increase synaptic concentrations of GABA (248). GABA has also been isolated from Valeria and extracts of Valeria have been reported to bind to GABA receptors in rat brain. Although Valeria has been reported to be active in rodent models of depression, there have been no efficacy trials in humans. The potential adverse effects of Valeria include the sensation of strangeness ( 247) and several cases of liver damage (e.g., central lobular necrosis) (249). Mutagenicity in bacteria has been reported and attributed to unstable, water-insoluble valepotriates ( 238). As a result of these reports, many, but not all, commercial preparations of Valeria use water-soluble extracts standardized for their content of valeric acid. 

Antibiotic resistance in bacteria is not a fixed property, and the degree of resistance detectable in the laboratory probably bears litde relationship to the resistance of the organism when growing in the intestinal tract of animals. The types of resistance that bacteria may develop to the action of antibiotics involve two distinct mechanisms mutation and inheritance. The former mechanism affects DNA sequence and results in the synthesis of a protein or macromolecule by the bacterial chromosome that differs from the original chemical entity, with the ability to interfere with the antibiotic activity. Because an antibiotic hinders a bacterium only after it has entered or crossed the cell wall and has bound to a target site, resistance can develop directly if the mutation has so altered the characteristics of the protein or macromolecule that the cell wall, receptor site, or transport mechanism is no longer friendly to the antibiotic. 

Various signaling systems used by animal cells also have analogs in the prokaryotes. As the full genomic sequences of more, and more diverse, bacteria become known, researchers have discovered genes that encode proteins similar to protein Ser or Thr kinases, Ras-like proteins regulated by GTP binding, and proteins with SH3 domains. Receptor Tyr kinases have not been detected in bacteria, but (P)-Tyr residues do occur in some bacterial proteins, so there must be an enzyme that phosphorylates Tyr residues. 

Although apparently derived from the bacterial two-component signaling system, the ethylene system in Arabidopsis is different in that the His kinase activity that defines component 1 in bacteria is not essential to the transduction in Arabidopsis. The genome of the cyanobacterium Anabaena encodes proteins with both an ethylene-binding domain and an active His kinase domain. It seems likely that in the course of evolution, the ethylene receptor of vascular plants was derived from that of a cyanobacterial endosymbiont, and that the bacterial His kinase became a Ser/Thr kinase in the plant. 

---