Denaturation and Renaturation
Denaturation is the loss of a protein's or DNA's three dimensional structure. The "normal" three dimensional structure is called the native state. Denaturing agents disrupt stabilizing factors. Destruction of a macromolecule's three-dimensional structure requires disruption of the forces responsible for its stability. The ability of agents to accomplish this disruption - denaturation - can be predicted on the basis of what is known about macromolecular stabilizing forces. Denatured macromolecules will usually renature spontaneously (under suitable conditions), showing that the macromolecule itself contains the information needed to establish its own three-dimensional structure. Denaturation is physiological - structures ought not to be too stable. 1. Double stranded DNA must come apart to replicate and for RNA synthesis. 2. Proteins must be degraded under certain circumstances. • To terminate their biological action (e.g., enzymes). • To release amino acids (e.g., for gluconeogenesis in starvation). Loss of native structure must involve disruption of factors responsible for its stabilization. These factors are: 1. Hydrogen bonding 2. Hydrophobic interaction 3. Electrostatic interaction 4. Disulfide bridging (in proteins)
Renaturation is the regeneration of the native structure of a protein or nucleic acid. Renaturation requires removal of the denaturing conditions and restoration of conditions favorable to the native structure. This includes: • Solubilization of the substance if it is not already in solution. • Adjustment of the temperature. • Removal of denaturing agents by dialysis or similar means. • In proteins, re-formation of any disulfide bridges. Usually considerable skill and art are required to accomplish renaturation. The fact that renaturation is feasible demonstrates that the information necessary for forming the correct three-dimensional structure of a protein or nucleic acid is encoded in its primary structure, the sequence of monomer units. Molecular chaperones are intracellular proteins which guide the folding of proteins, preventing incorrect molecular interactions. They do NOT appear as components of the final structures. Chaperones are widespread, and chaperone defects are believed to be the etiology of some diseases. Medical applications of chaperones may be expected to include things such as: • repair of defective human chaperones and • inhibition of those needed by pathogenic organisms.