Protein Structure and Synthesis: The Road to the Nobel Prize

How Do Proteins Fold? The Thermodynamic Hypothesis

Proteins fold into specific shapes to do their work. But how this happens was a major scientific mystery. Anfinsen wanted to know if positioning the right number of the right amino acids in the right sequence was enough to form a folded protein. For this work he used ribonuclease (RNase) from cows—obtained, interestingly enough, from a slaughterhouse.

This drawing from Anfinsen’s papers shows folded RNase on the left and denatured (unfolded) RNase on the right. The arrows face both ways to indicate that proteins can fold or unfold in a reversible process.

Eventually, Anfinsen’s conclusions became known as the Thermodynamic Hypothesis: the three-dimensional form of a protein is determined by the protein’s amino acid sequence and the environmental conditions in which the folding occurs.

Anfinsen unfolded RNase by dissolving its disulphide bonds, the bonds in its outer structures, and used special solvents, leaving the original amino acid chain intact. When he removed these chemicals, the protein automatically refolded into its active shape. This experiment demonstrated that the three-dimensional shape of a protein was determined by its amino acid sequence, confirming his hypothesis.

Image from The Molecular Basis of Evolution