Comparison of the elution of glycoproteins in normal and cystic fibrosis plasma from immobilized concanavalin A
Description
Cystic fibrosis is the most commonly occurring lethal genetic disease among the Caucasian population. Despite many years of extensive research, the biochemical defect in cystic fibrosis is still unknown, and there is no acceptable method for carrier detection. Abnormal glycoproteins or abnormalities in glycoprotein metabolism have been suggested as the underlying defect in cystic fibrosis In the present study, the elution patterns of normal and cystic fibrosis plasma glycoproteins from immobilized concanavalin A were compared. The results revealed highly significant differences in the elution profiles of (alpha)(,2)-macroglobulin, immunoglobulin G, and immunoglobulin M between normal and cystic fibrosis samples. These experiments demonstrated that the carbohydrate moieties of at least three plasma glycoproteins from cystic fibrosis patients were altered. These results were confirmed by comparison of the plasma glycoproteins in normal and cystic fibrosis samples by the novel technique of lectinofixation with concanavalin A The electrophoretic mobilities of the plasma glycoproteins eluted from immobilized concanavalin A were studied using immunoelectrophoresis. Striking differences in the electrophoretic mobilities of (alpha)(,2)-macroglobulin from normal and cystic fibrosis fractions were found. Differences in the electrophoretic mobilities of cystic fibrosis and normal immunoglobulin M were also observed. Since the polypeptide structures of purified normal and cystic fibrosis (alpha)(,2)-macroglobulin are known to be very similar, it was postulated that the differences in the electrophoretic mobilities of the cystic fibrosis plasma glycoproteins must be the result of alterations in their carbohydrate component. A difference in the number of charged sugar residues (or sialic acid) in the carbohydrate moieties could result in alterations of the electrophoretic mobilities of these glycoproteins With this possibility in mind, the relative sialic acid contents of normal and cystic fibrosis plasma glycoproteins were compared by measuring the binding ratios of the glycoproteins to limulin, a sialic acid-specific lectin. The (alpha)(,2)-macroglobulin and immunoglobulin M from cystic fibrosis plasma had significantly higher binding ratios to limulin than did normal plasma glycoproteins. Therefore, it was concluded that the higher sialic acid content of the cystic fibrosis glycoproteins results in a difference in their electrophoretic mobilities when compared to normal glycoproteins In summary, alterations in the carbohydrate moieties of cystic fibrosis glycoproteins were demonstrated by differences in binding and elution patterns of the glycoproteins from immobilized concanavalin A, differences in electrophoretic mobilities of glycoproteins in the eluted fractions, and alterations in binding ratios of the glycoproteins to limulin. The results indicate that there are alterations in the primary structures of the carbohydrate moieties of cystic fibrosis plasma glycoproteins. The alterations in primary carbohydrate structures may result in conformational changes in the glycoprotein molecules as well, which could cause altered functional properties in cystic fibrosis glycoproteins. This work supports the theory that abnormal glycoproteins and/or abnormalities in glycoproteins metabolism are closely related to the biochemical defect in cystic fibrosis