Interaction with unfolded protein

Adsorbents for biomacromolecules such as proteins have special properties. First, they need to have large pore sizes. A ratio of pore radius to molecule radius larger than 5 is desirable to prevent excessive diffusional hindrance (see Intraparticle Mass Transfer in this section). Thus, for typical proteins, pore radii need to be in excess of 10-15 nm. Second, functional groups for interactions with the protein are usually attached to the adsorbent backbone via a spacer arm to provide accessibility. Third, adsorbents based on hydrophilic structures are preferred to limit nonspecific interactions with the adsorbent backbone and prevent global unfolding or denaturation of the protein. Thus, if hydrophobic supports are used, their surfaces are usually rendered hydrophilic by incorporating hydrophilic coatings such as dextran or polyvinyl alcohol. Finally, materials stable in sodium hydroxide solutions (used for clean-in-place) are... 

Palleros, D. R., Welch, W. J., and Fink, A. L. (1991). Interaction of hsp70 with unfolded proteins Effects of temperature and nucleotides on the kinetics of binding. Proc. Natl. Acad. Sci. U.S.A. 88, 5719-5723. 

That is to say, the dynamics of interfacial water and its interactions with the protein surface are critical for the stability of protein structure. As soon as the strength of HBs at the interface between water and protein reaches a certain value, the 2D network around the protein that kept it folded collapses, allowing the macromolecule to increase its flexibility and to begin the denaturation process. We believe that the crossover phenomenon is a characteristic of the whole water-protein system the decreased interaction at the water-protein interface is the cause of both the crossover and the denaturation. On one hand, water becomes more mobile (increased diffusion constant) on the other, protein is not constrained by the HB network and can unfold. 

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