Multiple-site binding

Haring, R., and Kloog, Y. Multiple binding sites for phencyclidine on the nicotinic acetylcholine receptor from Torpedo ocel -lata electric organ. I ife Sci 34 1047-1055, 1984. 

Boulanger, Y. Schreier, S. Leitch, L. C. Smith, I. C. R, Multiple binding sites for local anesthetics in membranes Characterization of the sites and their equilibria by deuterium NMR of specifically deuterated procaine and tetracaine, Can. J. Biochem. 58, 986-995 (1980). 

B0 and B, are the amounts bound initially (at 1 = 0) and at specific times (t) after initiating dissociation. A plot of log,/l, against l is linear with a slope of -k, k may thus be estimated directly from the slope of this plot or may be obtained by nonlinear least-squares curve fitting to Eq. (5.12). It is always desirable to plot log,/) , against l to detect any nonlinearity that might reflect either the presence of multiple binding sites or the existence of more than one occupied state of the receptor. 

In the case of multiple binding sites or if the ligand-receptor complex isomerizes, the onset and offset curves will be multiexponential. It is generally assumed that nonspecific binding will occur rapidly, and this should certainly be so for simple entrapment in a membrane or cell pellet. If, however, specific binding is very rapid or nonspecific binding particularly slow (possibly... 

Closer least-squares fits can obviously be obtained by adopting more complicated models involving extra parameters. The use of more complicated models can, of course, be more readily justified if there is independent supporting evidence available (e.g., knowledge of multiple binding sites from functional studies). 

We chose to show the application of techniques employed to study supramolecular dynamics to host systems that have defined binding sites and, therefore, form host-guest complexes with defined stoichiometries. CDs were chosen because they represent a host with only one binding site, and therefore can be viewed as a model system for hosts with the lowest degree of complexity. DNA was chosen because it provides multiple binding sites for small molecules, i.e. intercalative and groove binding, while the DNA is structurally fairly well defined. 

Several predictions of this model have been experimentally supported, including the estimated heme-heme distance, and the protection of various (charged) groups on cytochrome c and ccp. However, as already noted, other theoretical models have suggested that multiple binding sites are possible within the cyt c ccp complex. The available spectroscopic and crystallographic data, reviewed in this section, tend to support a multisite model, rather than a highly specific lock and key structural model. 

Chelation The complexation of a metal cation by an organic ligand. Some ligands have multiple binding sites. Those with two sites are called bidentate ligands. 

An important question that needs to be addressed in any screening study is the determination of whether or not the ligand is non-covalently bound to the active site of the target protein. A number of simple GPC spin column ESI-MS screening methods have been developed to answer this question. These methods include the use of mutated proteins where the active site has been modified, GPC spin column/ESI-MS coupled with NMR (GPC spin column/MS/NMR) and displacement of known binders. Titration experiments with molar excesses of ligand to protein (described below in Section 2.3.3.2.4) can also be used to determine whether single or multiple binding sites are available in the protein. 

---