Receptor supramolecular complex

Figure 14. Simplified scheme of protein-protein interactions that transduce the sensory signal from the receptor supramolecular complex to the flagellar-motor supramol-eoular complex. Black arrows stand for regulated interactions. The scheme is not drawn to scale. (Taken with permission from Bren and Eisenbach [137].)...

While it is believed that the high-order structure of the receptor supramolecular complex has a role in chemotactic signaling, the composition and stoichiometry of the five different MCPs within these receptor supramolecular complexes are not known. If the seven-dimer model [427] is correct, the supramolecular complexes must differ from each other with respect to their MCP compositions. This is because the low-abundance receptors must interact with the high-abundance ones for their normal function [411, 422] and for being a part of the cluster [449]. Had the MCP compositions in all the receptor supramolecular complexes been the same, each complex should have been composed of at least 19-20 receptor dimers according to the known stoichiometry between the different types of MCPs [10-11 Tsr 6 Tar 1 Aer 1 Tap 1 Trg (Table 10)]. If, on the other hand, the lattice model [649] is correct, any MCP combination may be possible. The flexibility that this model... 

Figure 15. Hexagonal lattice model of the receptor supramolecular complex. Top Ran view, as seen from the cytoplasmic membrane looking into the cell. Bottom Schematic side view of the network. (Kindly provided by D. Bray, Cambridge University.)...

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. 

Signal transduction in response to chemoattractants Binding of a chemoattractant, say aspartate, to the receptor (Tar in the case of aspartate), results in subtle conformational changes of Tar with a consequent rearrangement of most, if not all, of the constituents of the receptor supramolecular complex. This rearrangement, which possibly involves stronger packing of the receptors [437], is sensed by the... 

According to these basic concepts, molecular recognition implies complementary lock-and-key type fit between molecules. The lock is the molecular receptor and the key is the substrate that is recognised and selected to give a defined receptor—substrate complex, a coordination compound or a supermolecule. Hence molecular recognition is one of the three main pillars, fixation, coordination, and recognition, that lay foundation of what is now called supramolecular chemistry (8—11). 

Since the dinuclear catalysts transform the intermolecular reaction of ethoxide with substrate into an intramolecular reaction within a supramolecular complex (Scheme 5.3), the effective molarity (EM) parameter, defined as kintra/fcinten strictly applies to the catalytic process at hand and, more in general, to processes in which molecular receptors promote the reaction of two simultaneously complexed reactants [35]. 

The VCD study of the 1,1 -binaphthyl derivatives [110] serves as an example of other structural information that can be obtained by the comparison of experimental and computed VCD. This method allows monitoring not only of absolute chirality of the molecule, but also of the contributions of individual functional groups to the spectra, molecular conformations or some important structural parameter. As an example, we discuss chiral binaphthyls which represent popular building blocks, chiral recognition receptors and catalyst. Controlling the angle between naphthyl planes is important when supramolecular complexes based on these compounds are built. 

Over the past decade, ESI-MS has been successfully used to study and characterize supramolecular complexes,56 58 after the detection of noncovalent receptor-ligand complexes by ESI-MS was first reported by Ganem et al. in 1991.59 A number of methods have been reported in the recent literature for the quantitative determination of noncovalent binding interactions using soft ionization mass spectrometry.60,61 However, to the best of our knowledge, supramolecular interactions have not yet been studied in a microreactor interfaced to a mass spectrometer. 

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