Protein Folding

After forming secondary structures, a protein folds into a specific three-dimensional shape that guides its function.

Many proteins form compact globular structures, while others form fibrous shapes.

Several chemical interactions guide this folding pattern.

First, hydrophobic interactions between amino acid side groups are a major contributor to protein compactness.

Nonpolar side chains move into the interior of the protein, forming a hydrophobic core away from water.

Many weak van der Waals attractions help stabilize this clustered hydrophobic core.

Amino acids with charged or polar side chains usually remain on the outside, where they interact with water.

Side chains with opposite charges can form ionic bonds, while side chains with similar charges repel each other.

Polar side chains can also form hydrogen bonds with water or with other polar side chains.

Lastly, disulfide bridges add extra stability to the protein structure.

These bonds form between two cysteine residues that may be far apart in the protein chain but come close together during protein folding. Each cysteine residue contains a sulfhydryl (–SH) group on its side chain.

The sulfur atoms of two cysteine side chains form a covalent disulfide bond that helps stabilize the folded protein.

These interactions help proteins maintain the precise shape needed for their biological function.