Table 1.

Compilation of X-ray Crystal Structures of Human C3 or Its Fragments, Either Free or Bound to Various Ligands Involved in Activation, Regulation, or Inhibition.

Class	C3 Protein	Ligand(s)	PDB IDa,b	Resolution (Å)	Authors	Citation
C3 Proper	C3	-	2A73	3.3	Janssen et al.	[12]
	C3a		4HW5	2.3	Bajic et al.	[86]
	C3b	-	2I07	4.0	Janssen et al.	[15]
	C3b	-	5F07	2.8	Forneris et al.	[43]
	iC3b1	hC3Nb1	6YO6	6.0	Jensen et al.	[87]
	C3c	-	2A74	2.4	Janssen et al.	[12]
	C3d	-	1C3D	1.8	Nagar et al.	[88]
C3 convertase	C3b	Factor B	2XWJ	4.0	Forneris et al.	[24]
	C3b	Factor B Factor D	2XWB	3.5	Forneris et al.	[24]
	C3b	Factor Bb S. aureus SCIN	2WIN	3.9	Rooijakkers et al.	[33]
	C3b	Factor Bb Factor P, monomeric formc S. aureus SCIN	6RUR	6.0	Pedersen et al.	[35]
	C345c	Factor P, monomeric formd	6S0B	2.3	van den Bos et al.	[36]
Regulators	C3b	MCP, CCP(1-4)	5FO8	2.4	Forneris et al.	[43]
	C3b	CR1, CCP(15-17)	5FO9	3.3	Forneris et al.	[43]
	C3b	DAF, CCP(2-4)	5FOA	4.2	Forneris et al.	[43]
	C3b	Factor H, CCP(1-4)	2WII	2.7	Wu et al.	[44]
	C3d	Factor H, CCP(19-20)	2XKW 3OXU	2.3 2.1	Kajander et al. Morgan et al.	[89] [90]
	C3b	mini-FHe, CCP(1-4)+(19-20)	5O32	4.2	Xue et al.	[46]
	C3b	mini-FHe, CCP(1-4)+(19-20) Factor I	5O35	4.2	Xue et al.	[46]
Receptors	C3c	CRIg, Ig(1)	2ICE	3.1	Wiesmann et al.	[23]
	C3b	CRIg, Ig(1)	2ICF	4.1	Wiesmann et al.	[23]
	iC3b	CR3, I-domain	7AKK	3.4	Fernandez et al.	[58]
	C3d	CR2, CCP(1-2)	3OED	3.2	van den Elsen et al.	[55]
	C3d	CR3, I-domain	4M76	2.8	Bajic et al.	[57]
Inhibitors	C3b	Variola virus SPICE, CCP(1-4)	5FOB	2.6	Forneris et al.	[43]
	C3c	S. aureus SCIN	3OHX	3.5	Garcia et al.	[22]
	C3c	S. aureus SCIN-B	3T4A	3.4	Garcia et al.	[66]
	C3b	S77, Fab fragment	3G6J	3.1	Katschke et al.	[68]
	C3b	hC3Nb1	6EHG	2.7	Jensen et al.	[67]
	C3c	Compstatin, 4W9A	2QKI	2.4	Janssen et al.	[75]
	C3b	Compstatin, Cp40	7BAG	2.0	Lamers et al.	[74]
	C3d	S. aureus Efb-C	2GOX	2.2	Hammel et al.	[18]
	C3d	S. aureus Ehp	2NOJ	2.7	Hammel et al.	[19]
	C3d	S. aureus Sbi, Domain IV	2WY7 2WY8	1.7	Clark et al.	[21]
	C3d	Factor H, CCP(19-20) B. burgdorferi OspE	5NBQ	3.2	Kolodziejczyk et al.	[91]

^aAs of this writing, there are 54 unique PDB depositions of crystal structures containing various forms of human C3.

^bIn general, only the first report of a structure determination is highlighted in this Table. However, certain structures representing particularly important features or significant improvements in either resolution or model quality are also included. Structures representing alternative crystal forms, site-directed mutants, or various ligands when unbound to C3 or its fragments are omitted in the interest of space.

^c,dFurther information on the nature and characterization of the monomeric form of properdin may be found in the publication of Pedersen et al. [34].

^eFurther information on the nature and characterization of the mini-FH protein may be found in the original manuscript by Schmidt et al. [47].