Table 1. Complex families in 2P2I_DB.

Class	#	Family	Complexa	Number of Inhibitorsb	Sourcec	Affinityd (nM)	Ref
I	1	BclXL/Bak	1bxl	8	PubMed	340	[27]
I	2	MDM2/p53	1ycr 1ycq	3	PubMed	600	[28]
I	3	XIAP BIR3/CASPASE 9	1nw9	2	PubMed	20	[29]
I	4	XIAP BIR3/SMAC	1g73	5	PubMed	420	[29]
I	5	ZipA/FtsZ	1f47	4	PubMed	20,000	[30]
II	6	Chagasin/Papain	3e1z	1	PDB	0.036e	[31]
II	7	E2/E1	1tue	1	PubMed	na	[32]
II	8	FKBP12/TGFR	1b6c	17	PDB	na	[33]
II	9	IL-2/IL-2R	1z92	8	PubMed	10	[34]
II	10	MMP1/TIMP1	2j0t	1	PDB	0.40e	[35]
II	11	MMP3/TIMP1	1oo9	1	PDB	0.22e	[36]
II	12	Subtilisin/Eglin C	1cse 1r0r 1to2	1	PDB	0.029	[37]–[39]
II	13	Thrombin/Protein C inhibitor	3b9f	1	PDB	na	[40]
II	14	Trypsin/Trypsin inhibitor	2uuy	3	PDB	0.02	[41]

PPIs were subdivided into class I that correspond to protein/peptide interactions with less than six segments at the interface (families 1–5) and class II that represent more globular interacting domains with more segments (families 6–14).

^aPDB code of protein/protein complexes.

^bNumber of inhibitors present in the database for a given protein/protein complex.

^cStructures were retrieved through exhaustive search of the protein databank (PDB) or literature data mining (PubMed).

^dDissociation constant (K_D) of the protein/protein complexes are indicated in nanomolar when available.

^eindicates Ki values.