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5.3 Regulating protein conformation and activity

5.3.1 Allosteric regulation

In many proteins, the binding of a particular ligand at one site affects the conformation of a second remote binding site for another ligand on the same protein. This effect is called allosteric regulation and it is an important mechanism by which a protein's binding capacity and/or its activity are regulated. Thus the switch between two different protein conformations can be controlled by binding of a regulatory ligand.

  • What example of allosteric regulation have you already encountered in this course?

  • Binding of Src to a phosphorylated tyrosine residue on another protein, via the SH2 domain, affects the conformation of the Src kinase domain, switching it to an active conformation.

Allosteric regulation is a feature of most proteins, including enzymes, receptors and scaffold proteins.

In biosynthetic enzyme pathways, where a series of distinct enzymes catalyse individual reactions in the pathway, a downstream product often acts as an allosteric regulator of an enzyme further upstream, switching it to an inactive conformation. This type of allosteric regulation is termed feedback inhibition and it serves to control the level of activity of the pathway as a whole, switching off production when product levels have reached the required level. Allosteric regulation of enzyme activity can be either positive or negative, switching an enzyme on or off respectively.


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