Recognition and Receptors

In order to form a crystal, molecules must aggregate in an orderly manner. This implies that intermolecular interactions have occurred in specific ways. It therefore follows that the crystal structure per se contains information on preferred modes of binding between the molecules in the crystalline state. In this Chapter we show how information on the most likely stereochemistries of interactions between functional groups in different molecules can be extracted from the three-dimensional coordinates of atoms listed in reports of crystal structure determinations. Three-dimensional structural data on binding stereochemistry may also be obtained from X-ray diffraction studies of the binding of small molecules to crystalline proteins and other macromolecules. These two types of information can be used, for example, to predict how drugs will interact with their biological receptors. 

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Kossiakoff, A. A. and De Vos, A. M., Structural basis for cytokine hormone-receptor recognition and receptor activation, Adv. Protein Chem., 52, 67-108, 1998. 

Although most exported bacterial proteins use this pathway, some follow an alternative pathway that uses signal recognition and receptor proteins homologous to components of the eukaryotic SRP and SRP receptor (Fig. 27-33). 

Unlike the steroid receptors, most of which function as homodimers, a second class of NRs function as heterodimers with the retinoid X receptor (RXR). Importantly, these receptors serve as sensors for metabolites such as fatty acids, oxysterols, and bile acids. Key elements of ligand recognition and receptor activation have been elucidated following structure-function analyses of several receptors in this family including the PPARs, liver X receptors (LXRs), and FXR. 

Because of their inherent stability, unique optical properties, and synthetic versatility, porphyrins and metalloporphyrins are excellent candidates for a variety of sensing-materials applications. Research in this area has focused on incorporation of synthetic porphyrins and metalloporphyrins into a variety of material matrices, such as polymers, glasses, and LB films. Substantial work has been done in the areas of solution and gas-phase. sensing, and highlights of both areas will be di.scussed. We will al.so briefly examine molecular recognition and receptor studies, becuase developments in these areas will further the development of porphyrin-based sensing materials. 

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