Unfolding of ribonuclease

Stelea SD, Pancoska P, Benight AS, et al. Thermal unfolding of ribonuclease A in phosphate at neutral pH deviations from the two-state model. Protein Sci. 2001 10 970-978. 

An explanation for these observances in the cases of ethanol and PEG may arise from hydrophobic interactions (i.e., methylene groups, methyl) with the unfolded state of the protein at elevated temperatures. This idea is supported by studies of the interaction of several alkylureas (methyl-, ACVdimethyl-, ethyl-, and butylureas) with the thermal unfolding of ribonuclease A, where it was shown... 

Yamamoto, K., Mizutani, Y., and Kitagawa, T. (2000) Nanosecond temperature jump and time-resolved Raman study of thermal unfolding of ribonuclease A, Biophys. J. 79, 485-495. 

ZhangJ, Peng X, Jonas A, andjonasj. NMR Study of the Cold, Heat and Pressure Unfolding of Ribonuclease A. Biochemistry 1995 34 8631-8641. 

J. Juneja and J. B. Udgaonkar, Characterization of the unfolding of ribonuclease A by a pulsed hydrogen exchange study evidence for competing pathways for unfolding. Biochemistry 41, 2641-2654 (2002). 

Wittemann A, BaUaufFM Temperature-induced unfolding of ribonuclease—a embedded in spherical polyelectrolyte brushes, Macromol Biosci 5 13—20, 2005. 

F. X. Schmid, R. Grafl, A. Wrba, and J. J. Beintema, Role of proline peptide bond isomerization in unfolding and refolding of ribonuclease, Proc. Natl. Acad Sci. U.S.A. 83, 872-876 (1986). 

Susceptibility to oxidation of disulfides built into proteins is strongly dependent on their location in the protein molecule (G3). Since the disulfides have a crucial role in maintaining protein tertiary structure, oxidation of certain —S—S— bridges may expose further disulfides and cause unfolding of the protein molcule. The final disulfide oxidation is a sulfone residue, which is stable and does not tend to reverse to sulfide. Therefore oxidative breakage of disulfides is irreversible. The spatial location of disulfides inside protein molecules influences their susceptibility to oxidation. The ribonuclease molecule has four —S—S— bonds, and at least three correctly located disulfide bonds are necessary to retain the ribonuclease enzyme properties. The compact ribonuclease molecule is relatively resistant to HOC1 oxidation (D18). 

Bigelow (1960) has found that all six of the phenolic groups of performic acid-oxidized ribonuclease behave normally, which is to be expected since the oxidized protein is believed to be highly unfolded. More interesting is his finding that a pepsin-inactivated preparation of ribonuclease can be prepared which contains five normal phenolic groups and one buried one. 

Haas E, McWherter C, Scheraga H. Conformational unfolding in the N-terminal region of ribonuclease A detected by nonradiative energy transfer Distribution of interresidue distances in the native, denatured, and reduced-denatured states. Biopolymers 1988 27 1-21. 

Kiefhaber, T. Quaas, R. Hahn, U. Schmid, F.X. Folding of ribonuclease Tj. 1. Existence of multiple unfolded states created by proline isomerization. Biochemistry 1990, 29, 3053-3061. 

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