One model of protein folding predicts that an unfolded protein quickly collapses from an extended random coil state to a low-volume conformation known as the molten globule. Within that state the protein's secondary and tertiary structures, including beta sheets and alpha-helices, form. This raises the question of what would happen if proteins were folded within confined spaces. Results are presented for two globular proteins, alpha-helical myoglobin (Mb) and cytochrome c (Cyt c), encapsulated within a porous sol-gel matrix. The sol-gels were formed by a reaction of tetramethylorthosilicate (TMOS) and water. It is known that in a sol-gel large motions of the protein, such as quaternary changes, are slowed, but it is not known if an unfolded protein could fold into its native state. Changing the pH or adding guanidinium-hydrochloride (Gdn-HCl) to the bathing solutions surrounding the gels induced unfolding or refolding depending on the initial conditions. The reversibility of the heme loss or insertion involved in the last folding steps for Mb was examined. Complete refolding of Mb was not achieved due to the migration of the heme within and out of the gels under unfolding conditions. In order to determine the percent of the heme escaping into solution as well as the percent of the protein refolding, basis spectra fitting was done. Conversion between the native state in Cyt c and a misfolded trapped state was also examined. These results are interpreted using the energy landscape model.
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