Hydration, charge, size, and shape characteristics of peptides from their CZE analyses

Abstract

A CZE model is presented for peptide characterization on the basis of well-established physicochemical equations. The effective mobility is used as basic data in the model to estimate relevant peptide properties such as, for instance, hydration, net and total electrical charge numbers, hydrodynamic size and shape, particle average orientation, and pH-microenvironment from the charge regulation phenomenon. Therefore 102 experimental effective mobilities of different peptides are studied and discussed in relation to previous work. An equation for the estimation of peptide hydration as a function of ionizing, polar, and non-polar amino acid residues is included in the model. It is also shown that the shape-orientation factor of peptides may be either lower or higher than one, and its value depends on a complex interplay among total charge number, molar mass, hydration, and amino acid sequence.

Analysis of the interplay among charge, hydration and shape of proteins through the modeling of their CZE mobility data

“…In Equation (1), [15,34]. In this work, we found appropriate to estimate, as a first approximation, a fractional weight averaged electrical permittivity within the domain of the protein through e 0 ¼ ed=ð1 þ dÞ þ e p =ð1 þ dÞ, where e p % 5 e o is an approximate value of the dry protein electrical permittivity [34] and d is the convergent value coming from the numerical iteration process described elsewhere [17]. Also e o is the vacuum electrical permittivity.…”

“…Here, in the PLLCEM the equivalent spherical model (ESM) of CZE is used again, which has been illustrated in [16,17,22] and validated in particular for spheroidal particles of low eccentricity, usually selected as prototype hydrodynamic shapes for proteins and peptides. The ESM has also been used widely in the literature and in basic texts to estimate diffusion and sedimentation coefficients [32,33].…”

“…Also activity coefficients g i are included as indicated in [17]. The evaluation of protein-effective charge requires the knowledge of actual pK i values of ionizing groups of side chains and ionizing terminal -COOH and -NH 2 groups [15,16,22,28].…”

“…The model is solved numerically by studying four proteins, for which CZEeffective mobilities and full protocol data are available in [15]. Also, emphasis is placed on the mathematical strategy to solve the resulting well-posed problem, by identifying the hydration number, estimated at a given pH, and the associated particle shape, through a consistent and convergent computational procedure presented in [15,17,22]. Then Section 3 analyses and discusses numerical results of the PLLCEM providing relevant physicochemical properties of the four proteins studied here.…”

“…At present CZE models are useful in the physicochemical characterization and interpretation of the effective mobility data of peptides and proteins [6][7][8][9][10][11][12][13][14][15][16]. One model type of interest is that considering the ''inverse problem'' [17] where, for a given protocol involving wellspecified bulk pH, ionic strength I, temperature T, electrical permittivity e and viscosity Z of the BGE, the experimental effective mobility is provided as the basic data to evaluate analyte properties such as, for instance, hydration, effective electrical charge, hydrodynamic size and shape, and pH-microenvironment, among others. This basic problem has associated the charge regulation phenomenon, also designated proton-binding cooperativity, which is always present around electrophoretically migrating particles [15][16][17][18][19][20][21][22][23][24].…”