Refolding conformational changes

Figure 8 Schematic representation of model for conformational changes during freezing, drying, and rehydration. N, native U, unfolded K, conformation equilibrium upon freezing, which shifts toward the native state in the presence of a cryoprotectant k, rate constant for refolding lc2, rate constant for formation of irreversibly denatured (aggregated) forms. (From Ref. 9.)...

The determination of binding and conformational changes leaves the question of the detailed structure of complexes unanswered. At present there is no absolute method for structure determination of protein-surfactant complexes apart from x-ray diffraction, which has only been applied to lysozyme with three bound SDS molecules [49]. X-ray diffraction requires a crystal, so in the case of lysozyme cross-linked triclinic crystals of the protein were soaked in 1.1 M SDS and then transferred to water or a lower concentration (0.35 M) of SDS to allow the protein to refold. It was necessary to use cross-linked crystals to prevent them dissolving when exposed to a high SDS concentration. The resulting denatured-renatured crystals were found to have three SDS molecules within a structure that was similar but not identical to that of native lysosyme. Neutron scattering has been applied in a few cases (see Sec. IX), but this is a model-dependent technique. 

Before long-term hemocompatibility can be expected for any material, the nature of polymer surface-protein interaction must be established in more detail the way in which the polymer surface alters itself (rotation of segments, side groups, chain refolding, etc.) in response to the protein species the way the protein is altered in conformation (if at all) upon adsorption by the surface and how this conformational change provokes platelet retention. Of course, longer-term ex vivo or in vivo studies also will be necessary. 

Once a protein is unfolded, even transiently, then isotope exchange is likely to occur rapidly, before it has chance to refold (A jn, > so ex Under such conditions, measurement of isotope exchange rates in folded proteins can give information about the rates of naturally occurring conformational changes. 

When the cytochrome is reduced, conformational changes take place in the form of refolding of the polypeptide chain both on the right and left sides of the porphyrin ring. The movements that are believed to be related to function involve a chain of residues (77-82) at the left side of the crevice. That portion of the chain contains a phenylalanine residue 82 that sticks out in the oxidized form. In the reduced forms, the sequence of residues 81-83 swings to the right... 

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