Revealing Functional Significance of Interleukin‐2 Glycoproteoforms Enabled by Expressed Serine Ligation

Comprehensive Summary Naturally occurring interleukin‐2 (IL‐2) is a pleiotropic glycoprotein that regulates immune responses by controlling the differentiation and homeostasis of T cells. Non‐glycosylated IL‐2 has been used in clinical settings for three decades. However, the function of the O ‐glycan of native IL‐2 remains elusive. Herein, to stress this issue, we report a highly efficient semi‐synthesis of homogeneous glycosylated IL‐2 with various glycoproteoforms on a multi‐milligram scale. The glycopeptide fragment was prepared by chemical synthesis and then merged with recombinant fragment via a serine ligation to generate the desired glycoprotein in a single operation. Biological evaluation of the homogenous glycoprotein library reveals that the activity of IL‐2 in activating individual T cell subset is glycan dependent, thus highlighting the possibility of further improving current clinical medicine.