Interplay between electrophoretic mobility and intrinsic viscosity of polypeptide chains

Abstract

The present work is motivated specifically by the need to find a simple interplay between experimental values of electrophoretic mobility and intrinsic viscosity (IV) of polypeptides. The connection between these two properties, as they are evaluated experimentally in a formulated dilute solution, may provide relevant information concerning the physicochemical characterization and separation of electrically charged chains such as polypeptides. Based on this aspect, a study on the relation between the effective electrophoretic mobility and the IV of the following globular proteins is carried out: bovine carbonic anhydrase, staphylococcal nuclease, human carbonic anhydrase, lysozyme, human serum albumin. The basic interpretation of the IV through polypeptide chain conformations involves two unknowns: one is the Flory characteristic ratio involving short-range intramolecular interactions and the other is the Mark-Houwink exponent associated with large-range intramolecular interactions. Here, it will be shown via basic and well-established electrokinetic theories and scaling concepts that the IV and global chain flexibility of polypeptides in dilute solutions may be estimated from capillary zone electrophoresis, in addition to classical transport properties. The polypeptide local chain flexibility may change due to electrostatic interactions among closer chain ionizing groups and the hindrance effect of their associated structural water.

Determination of electrokinetic and hydrodynamic parameters of proteins by modeling their electrophoretic mobilities through the electrically charged spherical porous particle

“…Then this parameter may be interpreted through the “hydrated chain fractal” model (as it was done for the AHP in ) to evaluate the packing and friction fractal dimensions of polypeptide chains, which in turns are crucial to examine polypeptide global conformations and scaling laws at different pH values. These scaling laws relate chain electrophoretic mobility to intrinsic viscosity, diffusion and sedimentation coefficients, and particle permeability in different polypeptide conformational states . In fact, the values of friction fractal dimension are shown below to be sensitive to the type of particle used to cover the collapsed to free draining chain states.…”

“…A number of them were achieved in BGEs having values of pH and ionic strength I involving the low charge regime, where a linear relationship between electrophoretic mobility and surface potential may be approximately established. Thus, in this regime ion polarization‐relaxation due to the flowing BGE around the electrically driven particle may be neglected . For a discussion on this aspect see, for instance, Refs.…”

“…To improve the prediction of Eq. when polypeptides are considered, the perturbed Linderstrøm‐Lang capillary electrophoresis model (PLLCEM) was proposed , where electrophoretic mobilities of aspherical hard particles (AHPs) were studied in the low charge regime, by defining the shape orientation factor . Here, the friction coefficient is evaluated either from AHP, such as spheroidal particles, or from hydrated chain fractals by defining the chain friction , where g f is the friction fractal dimension and a o is the average radius of N amino acid residues in the amino acid sequence (AAS) evaluated from their van der Waals radii.…”

“…From previous works, one concludes that AHP and hydrated chain fractals can model proteins by describing phenomena associated with their size, shape, average orientation during particle migration, electrical charge of weak ionizing groups confined at the particle surface , and particle hydration related to the degree of protein denaturation and the presence of ionizing polar and nonpolar amino acid residues. These characteristics were also shown to be relevant for the estimation of polypeptide diffusion coefficient and intrinsic viscosity .…”

“…By considering the above analysis, this work explores the possibility of using an electrically charged spherical porous particle (SPP) to model the electrophoretic mobility of polypeptides in the low charge regime. In this regard, the Hermans–Fujita analytic expression of μ p provided and widely analyzed by Ohshima is used and applied here specifically to proteins, in conjunction with theoretical aspects concerning the charge regulation phenomenon already described in the PLLCEM . Thus, in this first study on polyampholyte‐polypeptide SPP, particular numerical codes, where model parameters may also vary within the particle, are not considered .…”