Asn-linked sugar chain structures of recombinant human thrombopoietin produced in Chinese hamster ovary cells

Human thrombopoietin (TPO) that regulates the numbers of megakaryocytes and platelets is a heavily N- and O-glycosylated glycoprotein hormone with par tial homology to human erythropoietin (EPO). We prepared recombinant human TPO produced in Chinese hamster ovary (CHO) cells and analyzed the sugar ch ain structures quantitatively using 2-aminobenzamide labeling, sequential g lycosidase digestion and matrix-assisted laser desorption ionization time-o f-flight mass spectrometry (MALDI-TOF/MS). We found bi-, tri- and tetraantennary complex-type sugar chains with one or two N-acetyllactosamine repeats, which are common to recombinant human EPO produced in CHO cells. On the other hand, there were triantennary sugar ch ains with one or two N-acetyllactosamine repeats that were specific to the recombinant human TPO, and their distributions of branch structures were al so different. These results suggested that proximal protein structure shoul d determine the branch structure of Asn-linked sugar chains in addition to the glycosyltransferases subset.