Measuring protein stability in the GroEL chaperonin cage reveals massive destabilization.

All cells contain molecules known as proteins that perform many essential roles. Proteins are made of chains of building blocks called amino acids that fold to form the proteins' three-dimensional structures. Many proteins fold spontaneously into their well-defined and correct structures. However, some proteins fold incorrectly, which prevents them from working properly, and can lead to formation of aggregates that may harm the cell. To prevent such damage, cells have evolved proteins known as molecular chaperones that assist in the folding of other proteins. For example, a molecular chaperone called GroEL is found in a bacterium known as Escherichia coli. This molecular chaperone contains a cavity which prevents target proteins from forming clumps by keeping them away from other proteins. However, it remained unclear precisely how GroEL works and whether enclosing target proteins in its cavity has other effects. Moritella profunda is a bacterium that thrives in cold environments and, as a result, many of its proteins are unstable at room temperature and tend to unfold or fold incorrectly. To study how GroEL works, Korobko et al. used a protein from M. profunda called dihydrofolate reductase as a target protein for the chaperone. A clever trick was then used to determine the folding state of dihydrofolate reductase when inside the chaperone cavity. The experiments revealed that the environment within the cavity of GroEL strongly favors dihydrofolate reductase adopting its unfolded state instead of its folded state. This suggests that GroEL helps dihydrofolate reductase and other incorrectly folded target proteins to unfold, thus providing the proteins another opportunity to fold again correctly. Parkinson's disease, Alzheimer's disease and many other diseases are caused by proteins folding incorrectly and forming aggregates. A better understanding of how proteins fold may, therefore, assist in developing new therapies for such diseases. These findings may also help biotechnology researchers develop methods for producing difficult-to-fold proteins on a large scale.