Polyphosphates and Pyrophosphates of Pentopyranoses and Pentofuranoses as Allosteric Effectors of Human Hemoglobin: Synthesis, Molecular Recognition, and Oxygen Release

The concept of allosteric modulation: an overview

A brief historical overview of the concept of allosteric interaction is presented together with the different kinds of allosteric control recognized, in the past decades, with the model system of pentameric ligandgated ion channels. Multiple levels of allosteric modulation are identified that include sites distributed in the extracellular ligand binding domain (e.g. Ca2+ or benzodiazepines), the transmembrane domain (e.g. general anesthetic and various allosteric modulators) and the cytoplasmic domain, as potential targets for drug design. The new opportunities offered by the recent technological developments are discussed.

Allostery and the Monod-Wyman-Changeux model after 50 years

The Monod-Wyman-Changeux (MWC) model was conceived in 1965 to account for the signal transduction and cooperative properties of bacterial regulatory enzymes and hemoglobin. It was soon extended to pharmacological receptors for neurotransmitters and other macromolecular entities involved in intracellular and intercellular communications. Five decades later, the two main hypotheses of the model are reexamined on the basis of a variety of regulatory proteins with known X-ray structures: (a) Regulatory proteins possess an oligomeric structure with symmetry properties, and (b) the allosteric interactions between topographically distinct sites are mediated by a conformational transition established between a few preestablished states with conservation of symmetry and ligand-directed conformational selection. Several well-documented examples are adequately represented by the MWC model, yet a few possible exceptions are noted. New questions are raised concerning the dynamics of the allosteric transitions and more complex supramolecular ensembles.