© 2013 Elsevier Inc. All rights reserved. Cooperativity subsumes a diverse set of phenomena, including ligand-protein, protein-protein, and protein-DNA interactions, covalent modification of proteins, membrane assembly, and protein folding. In its usual sense the allosteric interaction promotes (positive cooperativity) or reduces (negative cooperativity) the expected function of a macromolecular complex. The principal manifestation of cooperativity is a sigmoidal (S-shaped) binding or reaction rate (response) curve that facilitates a nearly bimodal change of state over a narrow range of a control variable upon which a response depends. Sigmoid curves are typically modeled by the Hill equation. Curves with Hill coefficients greater than (positive cooperativity) or less than (negative cooperativity) 1 are usually considered diagnostic of cooperativity, and, with their principal response in a narrow range, are reminiscent of switch-like behavior, although they transition continuously and in a state of equilibrium between their unactivated and activated form without bistability. Cooperativity is in widespread use in the economy of cells including metabolic control, cell cycle control, ligand binding and transport, genetic switches (bistability), signaling, threshold phenomena, development, protein folding, and membrane assembly. Mathematical expressions incorporating cooperativity are frequent components of mathematical models of cellular processes, and may also be translated into design elements of switches and oscillators in synthetic biology.
- Brenner's Encyclopedia of Genetics: Second Edition
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