Stable hydrogen bonds (and salt bridges) between PD-1 and PD-L1 in the PD-1/PD-L1 interaction. Hot-spot acceptor and hot-spot donor (A); hot-spot acceptor and null-spot donor (B); null-spot acceptor and hot-spot donor (C); null-spot acceptor and null-spot donor (D).

Acceptora	Donor	Occupancyb
(A) H–H
PD-L1R125@O	PD-1Q75@NE2	0.90
PD-1Q75@OE1	PD-L1R125@N	0.51
(B) H–NH
PD-1E84@OE	PD-L1F19@N	0.69
PD-1E84@OE	PD-L1G120@N	0.64
(C) NH–H
PD-L1D122@OD	PD-1Y68@OH	0.98
*PD-1E136@OE	PD-L1R113@NH	0.94
PD-L1F19@O	PD-1K78@NZ	0.87
PD-L1A121@O	PD-1K78@NZ	0.80
PD-1E136@OE	PD-L1Y123@OH	0.79
PD-L1D26@OD	PD-1Q75@NE2	0.78
PD-L1A121@O	PD-1N66@ND2	0.68
(D) NH–NH
PD-L1D26@OD	PD-1S73@OG	0.57

^aThe salt bridge is labeled with *.

^bThe hydrogen bonds are determined by the default criteria (angle of acceptor hydrogen donor atoms greater than 135° and distance of acceptor donor atoms less than 3.0 Å) in the CPPTRAJ module of the AMBER14 package. Only hydrogen bonds with occupancy ≥ 0.50 are listed.