PDB 4ZQK — Structure of the complex of human programmed death-1 (PD-1) and its ligand PD-L1.
Reference structure for PD-L1, solved by X-ray crystallography and published as Reference/Zak 2015. Chain A is PD-L1 (this campaign's target); chain B is PD-1. See the 3D viewer on the target page for the interface itself.