Co-operative binding

E. Buxbaum. Co-operative binding sites for transported substrates in the multiple drug resistance transporter Mdrl. Eur J Biochem. 265 64—70 (1999). 

Vindimian, E., Robaut, C. and Fillion, G. (1983) A method for co-operative and non co-operative binding studies using non-linear regression analysis on a microcomputer, Journal of Applied Biochemistry 5, 261-268. 

A plot of VQ against [S] for an allosteric enzyme gives a sigmoidal-shaped curve. Allosteric enzymes often have more than one active site which co-operatively bind substrate molecules, such that the binding of substrate at one active site induces a conformational change in the enzyme that alters the affinity of the other active sites for substrate. Allosteric enzymes are often multi-subunit proteins, with an active site on each subunit. In addition, allosteric enzymes may be controlled by effector molecules (activators or inhibitors) that bind to a site other than the active site and alter the rate of enzyme activity. Aspartate transcarbamoylase is an allosteric enzyme that catalyzes the committed step in pyrimidine biosynthesis. This enzyme consists of six catalytic subunits each with an active site and six regulatory subunits to which the allosteric effectors cytosine triphosphate (CTP) and ATP bind. Aspartate transcarbamoylase is feedback-inhibited by the end-product of the pathway, CTP, which acts as an allosteric inhibitor. In contrast, ATP an intermediate earlier in the pathway, acts as an allosteric activator. 

Shanmugam et al., 1997 Sharkey et al., 1997 Morgan et al., 2000) and influence the stability of PBX-HOX complexes on co-operative binding sites that differ at position six (Shanmugam et al., 1997). These amino acids could modulate interactions with PBX by inducing conformational changes in the PBX homeodomain. 

In a mammalian system, transcriptional repression has also been ascribed to PBC-HOX heterodimers. Multimers of a PBX-HOX co-operative binding site (TGATTGAT) decrease reporter gene activity in transfected cells by comparison to an otherwise identical reporter bearing HOX monomer binding sites (Saleh et al., 2000b). However, at least some of this repression could be due to PBX homodimers and PBX MEIS or PBX-PREP heterodimers that are likely to bind multimerized PBC-HOX sites. Two instances of EXD-dependent but HOX-independent repression could be mediated by comparable EXD homodimers or EXD HTH heterodimers (Rauskolb and Wieschaus, 1994 Pinsonneault et al., 1997). 

Figure 20.2. The binding isotherm of a surfactant to a polymer without distinct hydrophobic moieties, giving the concentration of bound surfactant as a function of the free surfactant concentration, can be interpreted as a lowering of the surfactant CMC by the polymer, or a strongly co-operative binding...

The basis for the interaction between lipids and proteins is related to their amphiphilic nature and is due to their influence on the water structure, the so-called hydrophobic effect (Tanford, 1980). In general terms four alternative types of phases can occur in lipid-protein-water systems. An aqueous lipid solution can co-exist with a protein in the same solution alternatively a solution of molecular lipid-protein complexes can be formed. It is also possible that the lipid forms a liquid-crystalline phase (or an L2-phase) with water, such a phase can either solubilize a protein or co-exist with a protein solution. The first two interaction alternatives in water solution have been thoroughly discussed (Tanford, 1980). When the lipid concentration is below the CMC there is no interaction beside the eventual association of a few lipid molecules to the protein at certain high-affinity binding sites. At lipid concentrations above the CMC there is a so-called mass co-operative binding of numerous lipid molecules to each protein molecule and this leads to unfolding of the protein structure. 

Perlmutter-Ha5mian, B., Co-operative binding to macromolecules. A formal approach, Acc. Chem. Res., 1986, 19, 90-96. 

McGhee JD, von Hippel PH (1974) Theoretical aspects of DNA-protein interactions cooperative and non-co-operative binding of large ligands to a onedimensional homogeneous lattice. J Mol Biol 86(2) 469-489... 

Sodium dodecyl sulphate is bound co-operatively to most protein, the critical concentration for co-operative binding being about 25 % of the CMC. Non-ionic surfactants and the bile salts do not usually induce co-operative binding and do not usually, therefore, denature proteins, although dissociation into inactive or... 

Boraston, AB McLean, BW Chen, G Li, A Warren, RAJ Kilbum, DG. Co-operative binding of triplicate carbohydrate-binding modules from a thermophilic xylanase. Molecular Microbiology, 2002, 43(1), 187-94. 

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