Global conformations of proteins as predicted from the modeling of their CZE mobility data

Abstract

Estimations of protein global conformations in well-specified physicochemical microenvironments are obtained through global structural parameters defined from polypeptide-scale analyses. For this purpose protein electrophoretic mobility data must be interpreted through a physicochemical CZE model to obtain estimates of protein equivalent hydrodynamic radius, effective and total charge numbers, hydration, actual ionizing pK and pH-near molecule. The electrical permittivity of protein domain is also required. In this framework, the solvent drag on proteins is obtained via the characteristic friction power coefficient associated with the number of amino acid residues defining the global chain conformation in solution. Also, the packing dimension related to the spatial distribution of amino acid residues within the protein domain is evaluated and discussed. These scaling coefficients together with the effective and total charge number fractions of proteins provide relevant interpretations of protein global conformations mainly from collapsed globule to hybrid chain regimes. Also, protein transport properties may be estimated within this framework. In this regard, the central role played by the friction power coefficient in the evaluation of these properties is highlighted.

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

“…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.…”

“…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. Also in this framework the packing fractal dimension is as defined in . This simple CZE model yields approximate numerical values of useful polypeptide properties, apart from a H , Ω, f, and Z, when chain AAS and molar mass M are known.…”

“…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 .…”

“…In this regard, a typical fitting parameter is the effective particle charge number Z or the charge density ρ fix , which need to be estimated because, in principle, the number of charged groups in the particle is unknown. In contraposition to this situation, the knowledge of the polypeptide AAS provides a good estimation of Z value once the protocol pH and I of the BGE have been fixed and the protein charge regulation phenomenon has been included (see and citations therein).…”