Direct chemical modification and voltammetric detection of glycans in glycoproteins

Most of the proteins are glycosylated and glycoproteins are involved in physiological and pathological processes. Detection of changes in protein glycosylation is important in early diagnosis of different diseases, including cancer. Among the methods used for the analysis of the carbohydrate components (glycans) of glycoproteins, electrochemical methods were little applied. We propose a modification of glycans directly in glycoproteins using six-valent osmium complexes followed by glycan voltammetric determination at carbon electrodes. The electrochemical responses of two glycoproteins ribonuclease B and avidin as compared to their non-glycosylated counterparts were recorded either directly in the reaction mixture or after a simple purification step. Hundreds of femtomoles of the glycoprotein were sufficient for the analysis.