Reversible unfolding

Rief M, Gautel M, Oesterhelt F, Fernandez J M and Gaub FI E 1997 Reversible unfolding of individual titin immunoglobulin domains by AFM Science 276 1109... 

When a protein reversibly unfolds in solution, it enters a large and diverse ensemble of conformations known as the denatured state. Studies of this reaction over the past 40 years have suggested it is a single,... 

Alexa488 bound to IFABP monitored by steady-state fluorescence was fitted to a two-state reversible unfolding model. This modified protein is slightly less stable (midpoint of 4.5 M compared to 4.7 M for wild-type IFABP). 

ABF was probed through the reversible unfolding of a short peptide, deca-L-alanine, in vacuo [52] (see Fig. 4.10). The reaction coordinate, , is the distance separating the first and the last Ca carbon atom of the peptide chain. was varied between 12 and 32 A, thereby allowing the peptide to sample the full range of conformations between the native a-helical structure and the extended structures. The force acting along was accrued in bins 0.1 A wide. 

M. Rief, M. Gautel, E. Oesterhelt, M. Eemandez, and H.E. Gaub Reversible Unfolding of Individual Titin Immunoglobulin Domains by Afm. Science 276, 1109 (1997). 

D Network Polymers Containing Biomimetic Reversibly Unfolding Crosslinkers for Advanced Mechanicai Properties... 

Scheme 10.5 Synthesis of the UPy reversibly unfolding modular cross-linker.

Erickson HP. Reversible unfolding of fibronectin type III and immunoglobulin domains provides the structural basis for stretch and elasticity of titin and fibronectin. Proc Natl Acad Sci USA 1994 91 10114-10118. 

Kushner AM, Gabuchian V, Johnson EG, Guan Z. Biomimetic design of reversibly unfolding modular cross-linker to enhance mechanical properties of 3D network polymers. J Am Chem Soc 2007 129 14110. 

Scheme 10.5 Synthesis of the UPy reversibly unfolding modular cross-linker. Scheme 15.1 Schematic representation of the molecular imprinting process.

Andreu,J. M., Oliva, M. A., and Monasterio, O. (2002). Reversible unfolding of FtsZ cell division proteins from archaea and bacteria Comparison with eukaryodc tubulin folding and assembly./. Biol. Chem. 277, 43262-43270. 

Commonly, the thermal denaturation of proteins is often discussed in terms of the Lumry-Eyring model, which involves two steps reversible unfolding and irreversible alteration of the unfolded state to produce the final denatured state, which is unable to fold back to the native protein. 

The intrinsic fluorescence of the eight tryptophanyl residues in MBP can be used to measure its reversible unfolding/refolding reactions. When unfolded by incubation in a denaturant such as guanidinium hydrochloride, the side chains of the tryptophanyl residues are exposed to solvent and their fluorescence is quenched. On dilution of the denaturant, the subsequent refolding reaction can be monitored by the increase in fluorescence that results from burial of the side chains in the interior of the protein and their shielding from solvent (Liu et al., 1988, 1989). 

Conditions used for carrying out reversible unfolding equilibrium studies are quite different from the conditions in which thermostability is biologically or economically relevant, such as in detergent solution in a washing machine, under fermentation conditions, in the intestinal tract or in the bloodstream. 

Furthermore, it has been proposed that DMSO and alcohols can be utilized to stabilize reversibly unfolded states (Arakawa and Goddette, 1985 Bhattachar-jya and Balaram, 1997). For example, DMSO has been observed to stabilize a partially unfolded conformation of lysozyme (pH 3.0) (Bhattacharjyaand Balaram, 1997). Lysozyme in 10% DMSO showed little change in structure by nuclear magnetic resonance (NMR) when compared with aqueous conditions. The lysozyme structure in 50% DMSO resembled an early kinetic intermediate observed in the refolding process. Conversely, a highly unfolded structure in 100% DMSO has been reported, probably due to the polar aprotic nature of the solvent (Jackson and Mantsch, 1991). 

Cammack and Evans used another approach to investigate the FeS-A and FeS-B iron-sulfur proteins. They used guanidine.HCl in dimethylsulfoxide (DMSO) to reversibly unfold the polypeptide chain and at the same time maintain the iron-sulfur clusters intact. Their treatment of a PS-I subchloroplast particle... 

Irreversibility. The reasoning given above is also an oversimplification in another sense. Most of the results discussed concern loss of biological (e.g., enzyme) activity, and the activities then are determined after cooling to room temperature. It thus concerns an irreversible change, rather than reversible unfolding. The simplest case would be... 

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