Receptor supramolecular

Daryle H. Busch Lawrence, Kansas A Sampling of Multi-receptor Supramolecular Systems and Beginnings in the Chemistry of Orderly Entanglements... 

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... 

Yagi, S., M. Ezoe, I. Yonekma, T. Takagishi, and H. Nakazumi (2003). Diarylurea-linked zinc porphyrin dimer as a dual-mode artificial receptor Supramolecular control of complexation-faciUtated photoinduced electron transfer. J. Am. Chem. Soc. 125(14), 4068-4069. 

J. S. Fossey and T. D. James, Boronic Acid-Based Receptor, Supramolecular Chemistry, ed. R A. Gale and J. W. Steed, John Wiley Sons Ltd., Chichester, 2011, vol. 3. 

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). 

Fig. 1. Schematic representation of a receptor—substrate (host—guest) complex involving cavity inclusion of the substrate and the formation of different types of weak supramolecular interactions between receptor (hatched) and substrate (dotted).

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

The mechanism of recognition of most supramolecular entities (such as abiotic receptors) is the formation of several hydrogen bonds. Since heterocyclic tautomers possess both strong HBA and HBD properties (see Sections III,G, V,D,2, and VI,G), they are often used for this purpose. For instance, the hydrogen bond network formed by 5,5 -linked bis(2-pyridones) has been used by Dickert to obtain sensors (96BBG1312). 

Covalent and noncovalent combination of porphyrins as well as calix[4]arenes, resorcin[4]arenes including macroheterocyclic fragments, and cyclodextrins by construction of supramolecular artificial receptors 98EJ02689. 

Zhang Y, Gu FTW, Yang ZM et al (2003) Supramolecular hydrogels respond to ligand-receptor interaction. J Am Chem Soc 125 13680-13681... 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

Although non-covalent interactions of anions are one of the most actively explored areas of supramolecular chemistry [15], the anion sensing and recognition have up to now relied primarily on electrostatic binding or hydrogen bonding to the receptor [16,54-61]. However, recent UV-Vis and NMR spectral studies clearly reveal that complex formation takes place in the solutions between halides and neutral olefinic and aromatic it-acceptors such as those in Fig. 3 [23,62],... 

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