Protein before and after folding

Protein folding is the third stage in the development of protein structure.

The structure of a chaperonin. Chaperonins assist some protein folding.

Protein folding is how a protein gets its functional shape or 'conformation'. It is mainly a self-organising process. Starting from a random coil, polypeptides fold into their characteristic working shape. The structure is held together by hydrogen bonds.

The stages are:

1. Each protein exists as an unfolded polypeptide or random coil when translated from a sequence of mRNA to a linear chain of amino acids. This polypeptide lacks any developed three-dimensional structure (left hand side of the top figure).
2. Amino acids interact with each other to produce a well-defined three-dimensional structure, the folded protein (right hand side of the figure). This is known as the native state. The resulting three-dimensional structure is determined by the amino acid sequence (Anfinsen's dogma).

Without its correct three-dimensional structure a protein does not work. However, some parts of proteins may not fold: this is normal.