Allosteric Modulation

Whenever a ligand binds to a protein, the attracting forces between the ligand and the protein alter the protein's shape. For example, as a ligand approaches a binding site, these attracting forces can cause the surface of the binding site to bend into a shape that more closely approximates the shape of the ligand's surface.

Moreover, as the shape of a binding site changes, it produces changes in the shape of other regions of the protein, just as pulling on one end of a rope (the polypeptide chain) causes the other end of the rope to move. Therefore, when a protein contains two binding sites, the noncovalent binding of a ligand to one site can alter the shape of the second binding site and, hence, the binding characteristics of that site. This is termed allosteric (other shape) modulation (Figure 4-7a), and such proteins are known as allosteric proteins.

One binding site on an allosteric protein, known as the functional site (also termed the active site), carries out the protein's physiological function. The other binding site is the regulatory site, and the ligand that binds to this site is known as a modulator molecule

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART ONE Basic Cell Functions

(a) Allosteric modulation

Ligand-

Functional site

Activation of functional site

Protein

Regulatory site

Modulator molecule

(b) Covalent modulation

Functional site

(b) Covalent modulation

Covalent Modulation

Protein

I Phosphoprotein phosphatase l 2_

OH PO4

Protein

I Phosphoprotein phosphatase l 2_

OH PO4

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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