Other Chemotaxis Proteins

CheA is a histidine kinase that belongs to the superfamily of two-component regulatory systems, each constituting a sensor (a histidine kinase) and a response regulator [573], As mentioned above, CheA together with CheW and the MCPs forms a ternary complex at the bacterial poles [256, 463, 635], 

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Since the function of CheZ is to dephosphorylate CheY P, thereby terminating its interaction with the switeh, one could expect that CheZ will act primarily on switch-bound CheY P and will be randomly distributed in the cell or localized near the switeh. However, none of these expectations was found to be correct. First, Bren et al. found that CheZ cannot act on switch-bound CheY P it can only act on free CheY P [134], This is the consequence of the overlap, discussed in Section 7.5.2, between the interfaces of CheY that bind FliM and CheZ. Second, the distribution of CheZ in the cell is not random by analyzing cells expressing a functional, full-length CheZ fused with GFP or YFP, it was recently found that at least some of the CheZ molecules are localized in clusters at the cells poles [147, 677], CheZ being bound to CheAs [147]. This observation suggests that CheZ, like all the other cytoplasmic chemotaxis proteins, can be attached to the receptor supramolecular complex via CheA. This situation suggests that CheZ may have two different functions in chemotaxis one—still unknown—fullilled by CheZ localized at the receptor supramolecular complex, and one—fulfilled by non-localized CheZ— to terminate the interaction of CheY P with the switch. 

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. 

The other major arachidonic acid (AA) converting enzyme is an integral binding protein, 5-lipoxygenase, which is responsible for the initial transformation in a cascade of events towards the biosynthesis of leukotrienes. Leukotrienes are major mediators of numerous biological processes, including chemotaxis, and are implicated in hypersensitivity disorders like asthma. It was discovered in the early 1990s that another protein is necessary for the cellular synthesis of... 

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