Receptors chemotaxis-specific

There are still other important factors. Occupancy of the receptor by a ligand makes the receptor protein itself a substrate for the chemotaxis-specific methyl-transferase encoded by the cheR gene.62 70 71 This enzyme transfers methyl groups from S-adenosyl-methionine to specific glutamate side chains of the receptor to form methyl esters. In the aspartate receptor there are four such glutamate residues in a large cytoplasmic domain that includes the C terminus. 

In bacteria like E. coli and Salmonella, some chemotactic stimuli bind directly to chemotaxis-specific receptors, whereas others bind first to a primary receptor, which then interacts with a chemotaxis-specific receptor (Figure 12). The chemotaxis-specific receptors are the MCPs, mentioned in Section 5. The primary receptors are dual function in the sense that they are involved in both chemotaxis and transport of the stimulants. 

E. coli has five chemotaxis-specific receptors, MCPs, which sense a variety of stimuli. Of these receptors, Aer appears to be the most specific in... 

Figure 13. Schematic presentation of the structure of the best-characterized chemotaxis-specific receptor, Tar. The regions of interaction with the ligands and the proteins in the receptor complex are shown. For simplicity, helix superooiling is omitted, and the a-helices are represented by cylinders. Components that dock to the receptor in the assembled complex are shown schematically as ellipsoids and spheres. Cytoplasmic sites of methylation and demethylation (adaptation sites, residues 295, 3Q2, 309, and 491] are shown as small ovals. (Taken with permission from Falke and Hazelbauer (223], with slight modifications made by J.J. Falke.]...

Quiocho, F. A. and Ledvina, P. S. (1996) Atomic structure and specificity of bacterial periplasmic receptors for active transport and chemotaxis variation of common themes. 

During complement activation, several components are generated that serve as ligands for leukocytes (see 1.3.2.1-2) and that bind to specific receptors on the plasma membrane. Those complement components recognised by neutrophils may be soluble (e.g. C3a, C5a) and initiate chemotaxis and... 

Molecules (chemoattractants) that stimulate neutrophil-directed migration (chemotaxis) bind to distinct receptors on neutrophil plasma membranes (discussed in Chapter 38 of this text). Within seconds after chemoattractant binding, neutrophils exhibit rapid oscillations in actin polymerization and depolymerization (12,13). The shape changes accompanying chemoattractant binding depend on the duration and extent of F-actin polymerization (3). These quantitative studies of F-actin content were performed utilizing a flow cytometric assay that detects the fluorescence intensity of individual, fixed, permeabihzed cells that have been stained with F-actin-specific, fluorescent phallotoxins (14,15). 

Listed in Table 32-1 are some essential aspects of growth and differentiation. Some of them are obvious. Cohesion between molecules provides the basis of specificity. Receptors, whether they be enzymes, hormone receptors, or receptors for chemotaxis, are essential. They are usually activated by a conformational change that accompanies binding. A cell must have receptors that can respond to a variety of signals, which may come from within the cell, from the external medium, or from neighboring cells. The receptor-signal pairs are essential to local control, which provides the basis for all of development.4... 

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