Protein Denaturation and Renaturation

Protein Structure and Conformation

• A denatured protein can refold spontaneously into its original conformation when the denaturing solvent is removed, a process called renaturation.
• The fact that a denatured protein can refold into its correct conformation indicates that all the information necessary to specify the three-dimensional shape of a protein is contained in its amino acid sequence.
• Each protein normally folds into a single stable conformation, which can change slightly when the protein interacts with other molecules in the cell.
• Misfolded proteins can form aggregates that can damage cells and even whole tissues, and are thought to contribute to a number of neurodegenerative disorders.

Prions and Misfolded Proteins

• Misfolded proteins called prions can convert the properly folded version of the protein in an infected brain into the abnormal conformation, allowing the misfolded prions to spread rapidly from cell to cell.
• Prions are considered "infectious" because they can spread from an affected individual to a normal individual via contaminated food, blood, or surgical instruments.
• Prions can form aggregates, which can propagate and aggregate to form amyloid fibrils, disrupting brain cell function and causing neurodegenerative disorders.

Chaperone Proteins and Protein Folding

• Protein folding in a living cell is assisted by special proteins called chaperone proteins.
• Chaperones can bind to partly folded chains and help them to fold along the most energetically favorable pathway.
• Chaperones can also form "isolation chambers" in which single polypeptide chains can fold without the risk of forming aggregates in the crowded conditions of the cytoplasm.

Protein Shapes and Structures

• Proteins are the most structurally diverse macromolecules in the cell.
• Proteins can range in size from about 30 amino acids to more than 1000.
• The abundance of helices in proteins is due to the fact that a helix is a regular structure that resembles a spiral staircase, and is generated simply by placing many similar subunits next to one another.
• α helices and β sheets are structural features that can be generated by many different amino acid sequences.
• The handedness of a helix is not affected by turning the helix upside down, but is reversed if the helix is reflected in a mirror.