Comprehensive Glycomic and Glycoproteomic Analyses of Human Programmed Cell Death Protein 1 Extracellular Domain

Human programmed cell death protein 1 (hPD-1) is an essential
receptor
in the immune checkpoint pathway. It has played an important role
in cancer therapy. However, not all patients respond positively to
the PD-1 antibody treatment, and the underlying mechanism remains
unknown. PD-1 is a transmembrane glycoprotein, and its extracellular
domain (ECD) is reported to be responsible for interactions and signal
transduction. This domain contains 4 N-glycosylation
sites and 25 potential O-glycosylation sites, which
implicates the importance of glycosylation. The structure of hPD-1
has been intensively studied, but the glycosylation of this protein,
especially the glycan on each glycosylation site, has not been comprehensively
illustrated. In this study, hPD-1 ECD expressed by human embryonic
kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells was analyzed;
not only N- and O-glycosylation
sites but also the glycans on these sites were comprehensively analyzed
using mass spectrometry. In addition, hPD-1 ECD binding to different
anti-hPD-1 antibodies was tested, and N-glycans were found functioned
differently. All of this glycan information will be beneficial for
future PD-1 studies.