PubMed · 8746688
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I H Grant. 1996. Capillary electrochromatography.. https://doi.org/10.1385/0-89603-315-5%3A197
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The characterization of protein-folding kinetics with increasing chain length under various thermodynamic conditions is addressed using the capillarity picture in which distinct spatial regions of the protein are imagined to be folded or trapped and separated by interfaces. The quantitative capillarity theory is based on the nucleation theory of first-order transitions and the droplet analysis of glasses and random magnets. The concepts of folding funnels and rugged energy landscapes are shown to be applicable in the large size limit just as for smaller proteins. An ideal asymptotic free-energy profile as a function of a reaction coordinate measuring progress down the funnel is shown to be quite broad. This renders traditional transition state theory generally inapplicable but allows a diffusive picture with a transition-state region to be used. The analysis unifies several scaling arguments proposed earlier. The importance of fluctuational fine structure both to the free-energy profile and to the glassy dynamics is highlighted. The fluctuation effects lead to a very broad trapping-time distribution. Considerations necessary for understanding the crossover between the mean field and capillarity pictures of the energy landscapes are discussed. A variety of mechanisms that may roughen the interfaces and may lead to a complex structure of the transition-state ensemble are proposed.
The retardation of proteins in the M(r) range of 15-500 kDa in capillary electrophoresis conducted in semidilute solutions of the polymer polyethylene glycol (M(r) range 0.2-8.0 X 10(6)), was measured. The purpose was to test the predictions of the scaling theory with regard to the relation of retardation to (a) the M(r) of the polymer, (b) the concentration of the polymer, and (c) the radius of the protein particles. These predictions derive from a mechanism that relates retardation to the screening length of the polymer solution, viewed as the average distance between the entanglement points of polymer chains. For the molecular weight range from 60 to 500 kDa of (near) spherical proteins, the retardation was found to be related to polymer concentration c as mu/mu(0) = exp(-Ac0.69) where mu/mu(0) is the retardation expressed as the ratio between the mobility in polymer solution and that in free solution. The value of the exponent of 0.69 is in close agreement with the value of 0.75 predicted by the scaling theory. Parameter A was found (a) to scale as the 0.04th power of M(r) (polymer), approximating the predicted value of 0; and (b) to be proportional to particle radius as predicted. All measured values of retardation were independent of electric field strength in the range of 37-370 V/cm. Thus, experimental findings are consistent with the mechanism relating electrophoretic retardation to the screening length of the polymer network in the specified molecular weight range of proteins. Under the same conditions, log(mu/mu(0)) of proteins with M(r)'s less than 60 kDa (a) scales as the -0.06th power of M(r) (polymer), and (b) is proportional to polymer concentration, suggesting a retardation mechanism that is not related to the screening length.
To investigate the mechanism of formation of 2D arrays of protein macromolecules in liquid films we carried out model experiments with micron-sized latex particles. The direct observations revealed that the process of ordering is triggered by attractive lateral capillary forces due to the overlap of the menisci formed around the particles. Two types of lateral capillary forces, flotation and immersion, can be distinguished, and a theory of these interactions is developed. Similar forces are operative between inclusions (proteins) incorporated in lipid membranes. We develop an appropriate model of a lipid bilayer, which is described as an elastic layer (the hydrocarbon chain region) sandwiched between two Gibbs dividing surfaces (the two headgroup regions). The range of the interaction between two cylindrical inclusions turns out to be of the order of several inclusion radii. The results, which are in qualitative agreement with the experimental observations, can be applied to the interpretation of membrane processes and mechanisms such as protein aggregation in lipid membranes.