Fig. 1

The topological and functional features of human PD-1. a the compositions of the whole human PD-1 domains, where the PTM modified residues were noted by red asterisk and the disulphide bond was indicated. b The interaction model of the extracellular domain of human PD-1/PD-L1 complex (Green: human PD-1; Blue: human PD-L1). c The formation of the PD-1/PD-L1 complex triggers the negative signal for T cell exhaustion. d Sequence alignments between human and mouse PD-1 molecules, with a sequence identity (ID) of 65%. Green triangle indicated the sites located at both human and mouse PD-1’s the binding interfaces, while black asterisks indicated the sites only occurred at human PD-1 interface and red asterisks indicated the sites only occurred at mouse PD-1 interface