Allosteric regulation

Jump to navigation Jump to search

WikiDoc Resources for Allosteric regulation

Articles

Most recent articles on Allosteric regulation

Most cited articles on Allosteric regulation

Review articles on Allosteric regulation

Articles on Allosteric regulation in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Allosteric regulation

Images of Allosteric regulation

Photos of Allosteric regulation

Podcasts & MP3s on Allosteric regulation

Videos on Allosteric regulation

Evidence Based Medicine

Cochrane Collaboration on Allosteric regulation

Bandolier on Allosteric regulation

TRIP on Allosteric regulation

Clinical Trials

Ongoing Trials on Allosteric regulation at Clinical Trials.gov

Trial results on Allosteric regulation

Clinical Trials on Allosteric regulation at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Allosteric regulation

NICE Guidance on Allosteric regulation

NHS PRODIGY Guidance

FDA on Allosteric regulation

CDC on Allosteric regulation

Books

Books on Allosteric regulation

News

Allosteric regulation in the news

Be alerted to news on Allosteric regulation

News trends on Allosteric regulation

Commentary

Blogs on Allosteric regulation

Definitions

Definitions of Allosteric regulation

Patient Resources / Community

Patient resources on Allosteric regulation

Discussion groups on Allosteric regulation

Patient Handouts on Allosteric regulation

Directions to Hospitals Treating Allosteric regulation

Risk calculators and risk factors for Allosteric regulation

Healthcare Provider Resources

Symptoms of Allosteric regulation

Causes & Risk Factors for Allosteric regulation

Diagnostic studies for Allosteric regulation

Treatment of Allosteric regulation

Continuing Medical Education (CME)

CME Programs on Allosteric regulation

International

Allosteric regulation en Espanol

Allosteric regulation en Francais

Business

Allosteric regulation in the Marketplace

Patents on Allosteric regulation

Experimental / Informatics

List of terms related to Allosteric regulation

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Overview

In biochemistry, allosteric regulation is the regulation of an enzyme or protein by binding an effector molecule at the protein's allosteric site (that is, a site other than the protein's active site). Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are called allosteric inhibitors. The term allostery comes from the Greek allos, "other," and stereos, "space," referring to the regulatory site of an allosteric protein's being separate from its active site. Allosteric regulation is a natural example of feedback control.

Models of allosteric regulation

Most allosteric effects can be explained by the concerted MWC model put forth by Monod, Wyman, and Changeux, or by the sequential model described by Koshland, Nemethy, and Filmer. Both postulate that enzyme subunits exist in one of two conformations, tensed (T) or relaxed (R), and that relaxed subunits bind substrate more readily than those in the tense state. The two models differ most in their assumptions about subunit interaction and the preexistence of both states.

Concerted model

The concerted model of allostery, also referred to as the symmetry model or MWC- model, postulates that enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits. Thus all subunits must exist in the same conformation. The model further holds that in the absence of any ligand (substrate or otherwise), the equilibrium favors one of the conformational states, T or R. The equilibrium can be shifted to the R or T state through the binding of one ligand (the allosteric effector or ligand) to a site that is different from the active site (the allosteric site).

Sequential model

The sequential model of allosteric regulation holds that subunits are not connected in such a way that a conformational change in one induces a similar change in the others. Thus, all enzyme subunits do not necessitate the same conformation. Moreover, the sequential model dictates that molecules of substrate bind via an induced fit protocol. In general, when a subunit randomly collides with a molecule of substrate, the active site essentially forms a glove around its substrate. While such an induced fit converts a subunit from the tensed state to relaxed state, it does not propagate the conformational change to adjacent subunits. Instead, substrate-binding at one subunit only slightly alters the structure of other subunits so that their binding sites are more receptive to substrate. To summarize:

  • subunits need not exist in the same conformation
  • molecules of substrate bind via induced-fit protocol
  • conformational changes are not propagated to all subunits
  • substrate-binding causes increased substrate affinity in adjacent subunits

Allosteric activation and inhibition

Activation

Allosteric activation, such as the binding of oxygen molecules to hemoglobin, occurs when the binding of one ligand enhances the attraction between substrate molecules and other binding sites. With respect to hemoglobin, oxygen is effectively both the substrate and the effector. The allosteric, or "other," site is the active site of an adjoining protein subunit. The binding of oxygen to one subunit induces a conformational change in that subunit that interacts with the remaining active sites to enhance their oxygen affinity.

Inhibition

Allosteric inhibition occurs when the binding of one ligand decreases the affinity for substrate at other active sites. For example, when 2,3-BPG binds to an allosteric site on hemoglobin, the affinity for oxygen of all subunits decreases.[2]

Another good example is strychnine, a convulsant poison, acting as an allosteric inhibitor of glycine. Glycine is a major post-synaptic inhibitory neurotransmitter in mammalian spinal cord and brain stem. Strychnine acts at a separate binding site on the glycine receptor in an allosteric manner; i.e. its binding lowers the affinity of the glycine receptor for glycine. Strychnine thus inhibits the action of an inhibitory transmitter, causing convulsions.

Types of effectors

Many allosteric proteins are regulated by their substrate; such a substrate is considered a homotropic allosteric modulator, and is typically an activator. Non-substrate regulatory molecules are called heterotropic allosteric modulators and can be either activators or inhibitors.

Some allosteric proteins can be regulated by their substrates and by other molecules, as well. Such proteins are capable of both homotropic and heterotropic interactions.neat

See also


da:Allosterisk regulation de:Allosterie it:Regolazione allosterica he:אלוסטריה fi:Allosteerinen säätely

Template:Jb1


Template:WS