[[opthyphen]] THE EFFECT OF DENATURANTS ON PROTEIN MOBILITY. Jennifer L. H. Dunbar & Gregory K. Farber, Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802
Although chemical denaturants of proteins are frequently used in folding studies, their exact mechanism of action is still unknown. It is uncertain whether these denaturants act directly through binding to induce structural changes or whether they mediate unfolding indirectly through the solventl,2,3. Spectroscopic techniques such as circular dichroism provide useful information on the overall effects of adding a denaturant to a protein solution, but they do not yield exact structural details of the denaturant's interaction with the protein and solvent. Knowledge of these finer points of denaturation is essential in gaining a deeper understanding of both early events in denaturation and the variation proteins exhibit in their relative susceptibilities to denaturants.
We have used x-ray crystallography as a tool to probe changes in the structure of ribonuclease A in the presence of guanidinium. Ribonuclease A provides an excellent model because it has been extensively studied in terms of both its structure and folding. Four guanidiniums are observed in the denaturant structure, of which three form a cluster. The most important change noticed is a reduction in the mobility of the protein when guanidinium is added. Similar effects are seen in an analogous study of dihydrofolate reductase in the presence of urea.
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