Folding two-state

Factors that determine rate constants for two-state folding 601... 

Chyraotrypsin inhibitor 2 (CI2) folds rapidly by simple two-state kinetics that is, D N, with a r1/2of 13 ms.18,19 CI2 is a small 64-residue protein that has all its peptidyl-proline bonds in the favorable trans conformation.20 (There are, of course, additional slow cis —> trans peptidyl-prolyl isomerization events, which account for about 20-30% of the refolding amplitudes.) The occurrence of two-state kinetics does not prove that there are no intermediates on the folding pathway there could be intermediates that are present at high energy and are kineti-cally undetectable (see section B4). Two-state behavior has subsequently been found for many other small proteins. The simplicity of two-state folding kinetics provides the ideal starting point for the analysis and illumination of the basic principles of folding. 

Hydrogen exchange of a protein under denaturing conditions can be described by the following simple two-state (folded/unfolded) model ... 

Similar results (not shown) were obtained for numerous other C22A-FKBP segments. Observation of a common unfolding rate for each of many segments of the protein backbone further establishes a two-state (folded/unfolded) equilibrium for C22A-FKBP in 3.5 and 4.5 M urea. The unfolding rate constant, kunfold = 1 -8 +... 

A. Akmal, V. Munoz (2004) The nature of the free energy barriers to two-state folding. Proteins Struc. Fund. Bio. 47, pp. 142-152... 

D. Perl, C. Welker, T. Schindler et al. Conservation of rapid two-state folding in mesophiUc, thermophilic and hyperthermophilic cold shock proteins. Nature Structural Biology, 5 (1998), 229. 

Figure 1. The funnel shape Gibbs-free energy landscape of protein. The global minimum corresponds to the native state. Left There are no local minima. Two-state folding approximation Right There are many local minima. Presence of intermediate states, the red line corresponds to a folding pathway giving rise to a metastable intermediate state . ...

Figure 1. Relationship between the entropy function S(E) and the Helmholtz free-energy function F(E) at a given temperature. Panels A and A show a protein model with two-state folding character and show a protein model with a gradual folding process.

Perl, D., Welker, C., Schindler, T, Schroder, K., Marahiel, M.A., Jaenicke, R., Schmid, F.X. Conservation of rapid two-state folding in mesophOic, thermophilic and hyperthermophOic cold shock proteins, Nat. Struct. Biol. 1998, 5, 229-35. 

The chemical denaturant-dependent histidine hydrogen exchange protocol was initially developed and applied to several model protein systems including RNase A, myoglobin, and bovine carbonic anhydrase (BCA) II [32]. RNase A and myoglobin are known to have two-state folding behavior. BCA II is a non-two-state folding protein that is known to have a partially folded... 

Rhoades, E, Cohen, M, Schuler, B, and Haran, G, Two-state folding observed in individual protein molecules. Journal of the American Chemical Society 126 (2004) 14686-14687. 

K(T) = k-/k+). As is typical in such studies of assumed two-state folding, this equilibrium measurement can be complemented by a measurement of the observed kinetic rate constant k which is equal to the sum of the forward and reverse rate constants, k and k+ in this case. These two measurements therefore provide sufficient information to determine the values of the kinetic microscopic rate constants and therefore the relative size of the activation barrier A g] for forward and reverse transitions since fcj = Aexp —AG]/k T) where subscript i represents the opening or closing process, A is a pre-exponential factor [2] whose value depends on the system in question and k is Boltzmann s constant. 

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