Affinophoresis of pea lectin and fava bean lectin with an anionic affinophore, bearing rho-aminophenyl-alpha-D-mannoside as an affinity ligand

Quantitative evaluation of lectin-reactive glycoforms of α(1)-acid glycoprotein using lectin affinity capillary electrophoresis with fluorescence detection

α(1)-Acid glycoprotein (AGP) was previously shown to be a marker candidate of disease progression and prognosis of patients with malignancies by analysis of its glycoforms via lectins. Herein, affinity capillary electrophoresis of fluorescein-labeled AGP using lectins with the aid of laser-induced fluorescence detection was developed for quantitative evaluation of the fractional ratios of concanavalin A-reactive or Aleuria aurantia lectin-reactive AGP. Labeled AGP was applied at the anodic end of a fused-silica capillary (50 μm id, 360 μm od, 27 cm long) coated with linear polyacryloyl-β-alanyl-β-alanine, and electrophoresis was carried out for about 10 min in 60 mM 3-morpholinopropane-1-sulfonic acid-NaOH buffer (pH 7.35). Addition of the lectins to the anode buffer resulted in the separation of lectin-reactive glycoform peaks from lectin-non-reactive glycoform peaks. Quantification of the peak area of each group revealed that the percent of lectin-reactive AGP is independent of a labeling ratio ranging from 0.4 to 1.5 mol fluorescein/mol AGP, i.e. the standard deviation of 0.5% for an average of 59.9% (n=3). In combination with a facile procedure for micro-purification of AGP from serum, the present procedure, marking the reactivity of AGP with lectins, should be useful in determining the prognosis for a large number of patients with malignancies.

Capillary affinophoresis of pea lectin with polyliganded affinophores: a model study of divalent-polyvalent interactions

Affinophoresis is a type of affinity electrophoresis using an affinophore, a soluble ionic carrier bearing affinity ligand(s). It was reported previously that an affinophore, prepared by coupling multiple p-aminophenyl alpha-D-mannoside ligands to a part of the carboxyl groups of succinylated polylysine, specifically changed the mobility of pea lectin in agarose gel. The affinophoresis of this divalent lectin with the polyliganded affinophore was investigated by using capillary electrophoresis. Analysis of the mobility change of the lectin in the presence of differently modified affinophores showed that the affinity was larger for affinophores having higher ligand density. Analysis of the inhibition of the mobility change by a neutral ligand, with a known affinity constant for the lectin, allowed estimation of the contributions of monovalent and divalent interactions to the binding in the lectin-affinophore complex. The proportion of divalent complexes was greater for affinophores having higher ligand density. This approach to estimate the contribution of divalency in complex formation should be generally applicable to the analysis of divalent interactions with different techniques other than electrophoresis.

Progress in affinophoresis

The use of polyionic polymers as mobile affinity matrices in electrophoresis has led to the development of a specific separation method for biological substances, affinophoresis. The conjugate of a polyionic polymer and an affinity ligand is called an affinophore. Electrophoresis of proteins in the presence of an affinophore results in a change in the mobility of a specific protein due to the difference between the mobility of the protein and that of the protein-affinophore complex. Polylysine is useful as a base polymer of affinophores and has been used successfully as an anionic matrix after succinylation. Affinophoresis of proteases, lectins and antibodies has been carried out in agarose gel and the mobility of the protein having affinity to each ligand was specifically changed. Two-dimensional affinophoresis, in which an affinophore was included only in the second-dimensional electrophoresis, was effective for the separation of the components of a complex mixture of proteins even if the change of mobility was not large. Red blood cells were successively treated with homologous antiserum, biotinylated second antibody, avidin and biotinylated succinylpolylysine as an affinophore. Specific acceleration of the homologous cells to the antiserum was observed even when the affinophoresis was applied to mixed red blood cells from different species.

Affinophoresis of red blood cells: surface antigen-specific acceleration of electrophoresis

A method employing the technique of affinophoresis to increase the electrophoretic mobility of specific cells according to their surface antigens was developed. Red blood cells were treated consecutively with the maximum subagglutinating dose of an anti-red blood cell serum, a biotinylated second antibody, avidin and finally with a negatively charged biotin-affinophore which was prepared by coupling biotin to polylysine (average degree of polymerization, 270 or 1150), followed by complete succinylation. The electrophoretic mobility of cells was analyzed with an automatic cell electrophoresis analyzer. The use of a homologous anti-serum increased the electrophoretic mobility of rabbit, human and rat blood cells by 2.9, 1.7 and 1.6 times, respectively. A larger affinophore containing fewer biotin moieties was more effective. In the case of a mixture of red blood cells from two species, cells from only one species could be accelerated by using homologous antiserum, e.g., affinophoresis of a mixture of human and rat red blood cells by using either homologous antiserum gave two separate peaks on the histogram, whereas a single peak would be obtained in usual electrophoresis because there is little difference in the original migration velocities of the two cell types.

Influence of a soluble anionic polymer on the electrophoresis of proteins

The influence of a soluble anionic polymer on electrophoresis of proteins was studied in relation to the nonspecific ionic effect of an affinophore on application to affinophoresis. Zone electrophoresis of proteins was carried out in agarose gel in the presence of succinyl-poly-L-lysine (degree of polymerization, 120) by using three electrophoresis buffers differing in ionic strength (0.06, 0.12 and 0.18) and pH (7.0 and 7.9). Proteins migrated as distinct single bands even in the presence of the polymer. The mobility of cationic proteins towards the cathode was first decreased and then increased towards the anode as the polymer concentration increased, while that of anionic proteins was not affected. The dependence of the apparent mobility changes of the proteins on the concentration of the polymer was treated quantitatively in the same way as affinity electrophoresis. The extent of the ionic interaction between a cationic protein and the polymer could be estimated as an apparent dissociation constant. It greatly depended on the ionic strength of the electrophoresis buffer. Except for the extremely cationic proteins such as lysozyme, the ionic interaction with up to 0.1 mM of the polymer could be practically suppressed by the use of 0.1 M sodium phosphate buffer (pH 7.0).