Assisted Protein Folding

• Published in: The Journal of biological chemistry 1997-02, Vol.272 (6), p.3125-3128
• Main Authors: Ruddon, Raymond W., Bedows, Elliott
• Format: Article
• Language: English
• Subjects: Animals; Disulfides - chemistry; Glycosylation; Humans; Models, Biological; Molecular Chaperones - physiology; Protein Conformation; Protein Structure, Tertiary
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.6.3125

Historical Perspectives The pioneering work of the late Christian Anfinsen and his colleagues on the reoxidation of bovine pancreatic ribonuclease (RNase) to a native, biologically active enzyme in vitro after reduction of disulfide bridges and disruption of tertiary structure demonstrated that regeneration of native conformation of a purified protein can occur spontaneously in a test tube without the addition of any other co-factors or helper enzymes. This led to the still valid conclusion that "no special genetic information, beyond that contained in the amino acid sequence, is required for the proper folding of the molecule and for the formation of `correct' disulfide bonds". Of course, the story of protein folding goes back much further. A number of milestones can be noted. In 1911, Chick and Martin found that proteins could be denatured in vitro, and they distinguished that process from aggregation of the protein. In 1929, Wu postulated that protein denaturation was an unfolding process and that native protein structures involved regular, repeated patterns of folding into a three-dimensional network. Anson and Mirsky in 1931 and Anson showed that hemoglobin folding is reversible and that hemoglobin could be renatured in vitro to a form that had a native-like absorption spectrum, oxygen binding, and tryptic digestion pattern. Studies in the 1950s by Eisenberg and Schwert and by Schellman demonstrated that denaturation and renaturation are thermodynamic processes, involving a change in free energy and large changes in conformation between the denatured and native states. Even the early investigators realized that the protein folding processes that occurred in test tubes, although they could reconstitute native structure, were too slow to work inside cells. For example, even under optimized conditions of protein dilution, pH, and temperature, renaturation of RNase takes about 20 min, and RNase is a relatively simple monomeric protein. Renaturation of some multidomain proteins may take several hours in vitro, yet it is clear that all possible conformations could not be sampled on the way to native structure. Levinthal summed this up succinctly in the "Levinthal paradox" that can be stated as follows: if a given amino acid can assume approximately 10 different conformations, the total number of possible conformations in a polypeptide chain of 100 residues would be 10 super(100). The time that this could take would be well beyond the life span of an organis