Figure 2.

Molecular graphic representation of the competing binding modes from two crystallographic structures in the Protein Data Bank, 3OXU and 2XQW. Each binding site is described by one or more pairs of interacting chains (separated by a colon) from a specific crystallographic structure (PDB identifier of source noted). C3d is colored dim gray and specific residues associated with the acidic patch are colored in red while residues associated with the thioester domain are colored in yellow. FH is represented by CCP modules 19 and 20. FH CCP 20 is colored orange while CCP 19 is colored purple. At site 1, the binding configuration of C3d and FH varies between models (PDB 3OXU and 2XQW) suggesting apical flexibility.