Chaperones can correct protein misfolding, scientists say, but therapy is years away To do its job, whether it is an enzyme, ion channel, or structural molecule, a protein must fold into a very specific shape--its conformation. For this reason, mutations that change how a protein folds can have profound health effects, causing either a loss of function as in cystic fibrosis or a deleterious "gain of function" as happens in many neurodegenerative diseases in which protein misfolding results in the formation of harmful inclusion bodies.Researchers now believe that protein misfolding could be involved in up to half of all human diseases, says prion researcher Susan Lindquist (Whitehead Institute for Biomedical Research, Cambridge, MA, USA). In addition to its involvement in cystic fibrosis and neurodegeneration, Lindquist notes, protein misfolding "is responsible for many cancers". Many cancer-causing mutations occur in proteins that are key regulators of growth and differentiation, she explains, and when these proteins misfold they can either lose normal activity or gain abnormal activity. Lindquist believes that there is "a very strong potential" for treating human disease by finding ways to deal with misfolded proteins. But neither she nor other scientists studying protein folding claim that this quest will be easy.Since the 1950s, scientists have known that the information necessary for a protein to fold properly is encoded in its aminoacid sequence. However, in the past 15 years, researchers have discovered that matters are not quite that simple within cells. "In 1987, we were studying how proteins got into mitochondria", says Arthur Horwich (Yale University School of Medicine, New Haven, CT, USA). "It was becoming clear that for this to happen, proteins had to unfold so that they could get through the mitochondrial membranes rather like a strand of spaghetti. The question we and others asked was 'Do proteins spontaneously refold once they get into mitochondria or is some sort of machine needed?'"Cells were soon discovered to have several such machines--called chaperones--that assist protein folding particularly when cells are exposed to stresses such as heat.