Question

1. Describe how effectors of allostery regulate protein function based on positive and negative changes that take place in the protein.

2. Describe how ligand binding controls protein function by allostery

3. Describe the regulation of protein function based on quaternary structure

4. Propose how an inhibitor may or may not be an allosteric effector based on competitive, noncompetitive, and uncompetitive inhibition

Describe quaternary structure based on subunits.

Answer 1

1. Enzyme functioning gets affected by binding of a small allosteric molecule. This brings subtle changes in the enzyme tertiary and quarternary structures. These changes can cause alterations in enzyme or protein activity. These effector molecules bind to a site called allosteric site bring changes in the structure of the protein molecule. Binding of the allosteric effector can activate the protein activity or inhibit the activity of the protein. If the allosteric effector activates, the protein function will increase. This is positive allosteric effect. Negative allosteric effect will inhibit the protein activity.

2. When a ligand binds to the allosteric site of the enzyme, the tertiary and quarternary structures of the proteins gets slightly disturbed. This disturbance in the protein structure will effect the functioning of the protein.

3. Quarternary structure is formed when more than one tertiary proteins come together to form a functional protein. Quarternary structures allow protein to have number of functions by bringing conformational changes in the polypeptide fo the proteins. Each individual sub unit can change shape and bring a different function. This is how quarternary structures are involved in regulation of proteins too.

4. Proteins have 3 dimensional structure with active sites present on the surface. The active site is complimentary to a particular substrate molecule. When the substrate and enzyme bind to form a temporary complex, it reduces the activation energy to speed up a chemical reaction. An inhibitor molecule may be structurally similar and complimentary to active site of the enzyme. In such a case, the substrate and the inhibitor both compete for the same active site. In such a case this is called competitive inhibitor and the process is competitive inhibition.

An inhibitor of an enzyme may bind to the allosteric site instead of active site. In such a case inhibitor is not competiting with the active site of the enzyme and hence it is non-competitive inhibition.

Un competitive inhibitor binds to substrate - enzyme complex. The inhibitor is not binding to the allosteric site here.

5. A quarternary structure of the protein occurs when more than one tertiary proteins come together and interact to form quarternary structure. HEmoglobin is one such example. Globin part of the hemoglobin is quarternary protein. It is made of 4 polypeptides. Two alpha and two beta polypeptide units. Each unit is attached to a heme ring which has cetrally located Fe+ ion. O2 binds to the Fe+ ions. 4 Fe+ ions present in one hemoglobin molecule which allows carrying 4 O2 molecule at time by one hemoglobin molecule.