Search for:. Denaturation and Protein Folding. Learning Objective Discuss the process of protein denaturation. Key Points Proteins change their shape when exposed to different pH or temperatures. The body strictly regulates pH and temperature to prevent proteins such as enzymes from denaturing. Some proteins can refold after denaturation while others cannot. Chaperone proteins help some proteins fold into the correct shape.
When Jello is heated, its structure is altered so that it is no longer a gel but a liquid. If the denaturing conditions reversed by cooling in the refrigerator, the protein reforms into its original gel structure. The example on the left is from the prion protein with the salt bridge of glutamic acid and lysine In this case a very small loop is made because there are only three other amino acids are between them. The salt bridge has the effect of straightening an alpha helix.
The denaturation reaction on the salt bridge by the addition of an acid results in a further straightening effect on the protein chain as shown in the graphic on the left. Heavy metal salts act to denature proteins in much the same manner as acids and bases. Since salts are ionic they disrupt salt bridges in proteins.
The reaction of a heavy metal salt with a protein usually leads to an insoluble metal protein salt. This reaction is used for its disinfectant properties in external applications.
For example AgNO 3 is used to prevent gonorrhea infections in the eyes of new born infants. Silver nitrate is also used in the treatment of nose and throat infections, as well as to cauterize wounds. Mercury salts administered as Mercurochrome or Merthiolate have similar properties in preventing infections in wounds.
This same reaction is used in reverse in cases of acute heavy metal poisoning. In such a situation, a person may have swallowed a significant quantity of a heavy metal salt. As an antidote, a protein such as milk or egg whites may be administered to precipitate the poisonous salt. Then an emetic is given to induce vomiting so that the precipitated metal protein is discharged from the body. Quiz: Name other amino acids that may engage in salt bridges. Other answers are possible.
Answer Only two acids available asp and glu Amines? Answer Three amines are available lys, arg, and his. Heavy metals may also disrupt disulfide bonds because of their high affinity and attraction for sulfur and will also lead to the denaturation of proteins. Disulfide bonds are formed by oxidation of the sulfhydryl groups on cysteine. Different protein chains or loops within a single chain are held together by the strong covalent disulfide bonds. Both of these examples are exhibited by the insulin in the graphic on the left.
If oxidizing agents cause the formation of a disulfide bond, then reducing agents, of course, act on any disulfide bonds to split it apart.
Reducing agents add hydrogen atoms to make the thiol group, -SH. The reaction is:. Insulin Protein - Chime in new window. Amino Acids. The properties of this ensemble depend sensitively on the solution conditions. There is now considerable evidence that even in strong denaturants such as 6M GuHC1 and 9M urea, some structure may remain in protein chains. Under milder or physiological conditions, the denatured states of most proteins appear to be highly compact with extensive secondary structure.
Both theoretical and experimental studies suggest that hydrophobic interactions, chain conformational entropies, and electrostatic forces are dominant in determining this structure. The denaturation reaction of many proteins in GuHC1 or urea can be most simply modelled as a two-state transition between the native structure and a relatively compact denatured state, which then undergoes a gradual increase in radius on further addition of denaturant.
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