The search for folding intermediates and the mechanism of protein folding

My research began with theory and methods for ultracentrifugal studies of proteins, first at the University of Wisconsin, Madison, with Bob Alberty and Jack Williams, then at Oxford University with A.G. ("Sandy") Ogston, and finally back at Wisconsin with Williams and Lou Gosting. In 1959 I joined Arthur Kornberg's Biochemistry Department at Stanford University. Our first work was physical studies of DNA replication and then DNA physical chemistry, and DNA studies ended with the energetics of DNA twisting. In 1971 we began to search for protein folding intermediates by fast-reaction methods. We found the slow-folding and fast-folding forms of unfolded ribonuclease A, which led to the understanding that proline isomerization is sometimes part of the folding process. Using hydrogen exchange as a probe, we found the rapid formation of secondary structure during folding and used this to provide an NMR pulse labeling method for determining structures of folding intermediates. Our studies of peptide helices provided basic helix-coil parameters, also evidence for hierarchic folding, and further indicated that peptide hydrogen bonds are important in the energetics of folding.