Cooperative conformational transition

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

Haley MM, Pak JJ, Brand SC (1999) Top Curr Chem 201 81 HOger S (1999) J Polym Sci A Polym Chem 37 2685 Bunz UHF, Rubin Y, Tobe Y (1999) Chem Soc Rev 28 107 Faust R (1998) Angew Chem Int Ed 37 2825 Moore JS (1997) Acc Chem Res 30 402 Zhao D, Moore JS (2003) Chem Commun 807 Nelson JC,Saven JG,Moore JS,Wolynes PG (1997) Science 277 1793 Shetty AS, Zhang J, Moore JS (1996) J Am Chem Soc 118 1019 Prince RB,Saven JG,Wolynes PG,Moore JS (1999) J Am Chem Soc 121 3114 Hill DJ, Moore JS (2002) Proc Natl Acad Sci USA 99 5053 Cantor CR, Schimmel PR (1980) Biophysical chemistry. Freeman, San Francisco Prince RB (2000) Phenylene ethynylene foldamers cooperative conformational transition, twist sense bias, molecular recognition properties, and solid-state organization. PhD thesis. University of Illinois at Urbana-Champaign... 

N 153 Analysis of Cooperative Conformational Transitions hi Cellulose and Amylose Triearbanilates"... 

Hen egg-white lysozyme, lyophilized from aqueous solutions of different pH from pH 2.5 to 10.0 and then dissolved in water and in anhydrous glycerol, exhibits a cooperative conformational transition in both solvents occurring between 10 and 100°C (Burova, 2000). The thermal transition in glycerol is reversible and equilibrium follows the classical two-state mechanism. The transition enthalpies AHm in glycerol are substantially lower than in water, while transition temperatures Tm are similar to values in water, but follow similar pH dependences. The transition heat capacity increment ACp in glycerol does not depend on the pH and is 1.25 0.31 kj (mol K) 1 compared to 6.72 0.23 kj (mol K)-1 in water. Thermodynamic analysis of the calorimetric data reveals that the stability of the folded conformation of lysozyme in glycerol is similar to that in water at 20-80°C but exceeds it at lower and higher temperatures. 

An extreme case that has received attention is that of a cooperative conformational transition examplified by the coil-helix (c h) transition that occurs in poly-a-aminoacids. Whereas the polypeptide chain is quite flexible when it exists as a random coil, the rigid helical form may bring about formation of a liquid crystalline phase, as discussed above, if its concentration is sufficient. The conformational transition and the phase transition may therefore be coupled. The helix-coil transition may then acquire the character of a first-order phase transition, owing to generation of the liquid crystalline phase. 

Segmental motions of P(3HB) and P(3HB-co-27%3HV) in chloroform-d solution have been studied by measuring NMR relaxation times and NOE factors as a function of temperature [72, 73]. Analysis of the relaxation data on the basis of the Dejean-Laupretre-Monnerie (DLM) model, which describes the dynamics of polymer chains [74], indicates that the local dynamics of a comonomer unit, e.g., 3HB, are independent of the presence of a nearby 3HV unit and vice versa that segmental motion of the P(3HB-co-27%3HV) copolymer described by cooperative conformational transitions [73] is similar to that for the P(3HB) homopolymer [72]. These motional characteristics of the P(3HB-co-3HV) copolymer chain are consistent with the conformational characteristics derived by the analysis of spin coupling as shown in Section 21.2.2.3 [63] and are consistent with the occurence of cocrystallization in this copolymer system. 

Thus, we assume that the observing in the radical polymerization of MAG microheterogeneity is the consequence of the fact that MAG monomer at the expense of guanidine groups content leads to coagulation of PMAG propagating chains as a result of cooperative conformational transition. 

Weber and Helfand (8) characterize segmental motion in terms of a correlation time for single conformational transitions, tq, and a correlation time for cooperative conformational transitions, tj. This model has been applied to nuclear spin relaxation before (5) and the form of the spectral density for a composite segmental motion and anisotropic internal rotation is written... 

Enzyme inactivation has been frequently described by a very simple one-stage mechanism in which it is assumed that the enzyme suffers a highly cooperative conformational transition from a native active stiucture to an unfolded completely inactive form (Henley and Sadana 1985). This transition is represented by a hypothetical chemical reaction ... 

In the absence of a cooperative conformational transition, for many polysaccharide polyelectrolytes a linear dependence of [rj] upon I Ms observed, with the slope diminishing with the charge density associated to the polysaccharide chain (Figure 12.2.13). A theory has been presented for an estimation of the relative stiffness of the molecular chains by Smidsrod and Haug, which is based on the Fixman s theory and Mark-Houwink equation. The chain stiffness parameter is estimated from the normalized slope B of [r ] vs. the inverse square root of the ionic strength ... 

Prince, R. B. Saven, J. G. Wolynes, P. G. Moore, J. S. Cooperative conformational transitions in phenylene ethynylene oligomers chain-length dependence. J. Am. Chem. Soc. 1999, 727,3114-3121. 

Experimentally, to a very good approximation, many proteins exhibit a highly cooperative conformational transition that is well described by a two state model. Furthermore, in a number of proteins, the cooperativity in protein folding arises on passage from the molten globule state to the native... 

The existence of the hydrophobic-core collapse, which is accompanied by the creation of a polar shell that screens the hydrophobic core from the solvent, renders the folding behavior of a heteropolymer different from crystalhzation or amorphous transitions of homopolymers. The reason is the disorder induced by the sequence of different monomer types. The hydrophobic-core formation is the main cooperative conformational transition which accompanies the tertiary folding process of a single-domain protein. 

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