Chemotaxis, specificity

Zhou, H. Dahlquist, F.W. Phosphotransfer site of the chemotaxis-specific protein kinase CheA as revealed by NMR. Biochemistry, 36, 699-710 (1997)... 

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.]...

McEvoy, M.M., Zhou, H.J., Roth, A.F., Lowry, D.F., Morrison, T.B., Kay, L.E. and Dahlquist, F.W. (1995). Nuclear magnetic resonance assignments and global fold of a CheY-binding domain in CheA, the chemotaxis-specific kinase of Escherichia coli. Biochemistry 34,13871—13880. 

Is sperm chemotaxis specific, i.e., are the chemoattractants specific for each species or are there chemoattractants common to several species There is no single answer to this question. With some exceptions, species specificity appears to be the rule in marine species [102, 103]. There, the gametes are released in to seawater, and gametes of different species may be in close proximity. Therefore, in these cases, chemotaxis may be needed as one of the means to avoid interspecies fertilization. Indeed, in some marine groups (e.g., sea urchins, hydromedusae and certain ophiuroids), the specificity of sperm chemotaxis is very high. In other groups (e.g., starfish), the specificity is at the family level and, within the family, there is no specificity. In contrast, in mollusks, there appears to be no specificity at all ([35,102,103] and references therein). 

Vinca alkaloids (vincristine, vinblastine, vindesine) are derived from the periwinkle plant (Vinca rosea), they bind to tubulin and inhibit its polymerization into microtubules and spindle formation, thus producing metaphase arrest. They are cell cycle specific and interfere also with other cellular activities that involve microtubules, such as leukocyte phagocytosis, chemotaxis, and axonal transport in neurons. Vincristine is mainly neurotoxic and mildly hematotoxic, vinblastine is myelosuppressive with veiy low neurotoxicity whereas vindesine has both, moderate myelotoxicity and neurotoxicity. 

Vinca alkaloids are derived from the Madagascar periwinkle plant, Catharanthus roseus. The main alkaloids are vincristine, vinblastine and vindesine. Vinca alkaloids are cell-cycle-specific agents and block cells in mitosis. This cellular activity is due to their ability to bind specifically to tubulin and to block the ability of the protein to polymerize into microtubules. This prevents spindle formation in mitosing cells and causes arrest at metaphase. Vinca alkaloids also inhibit other cellular activities that involve microtubules, such as leukocyte phagocytosis and chemotaxis as well as axonal transport in neurons. Side effects of the vinca alkaloids such as their neurotoxicity may be due to disruption of these functions. 

As already mentioned, molecular cross talk seems to be the prerequisite mechanism for most of root microbial infections. Indeed the initial step of any root colonization involves the movement of microbes to the plant root surface bacterial movement can be passive, via soil water flux, or active, via specific induction of flagellar activity by plant released compounds (chemotaxis) (Chaps. 4 and 7). Other important steps are adsorption and anchoring to the root surface. 

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