C. The reported mutagenesis data on MCP CCP3 and CCP4 (data from Liszewki et al. (Liszewski et al, 2000)) are consistent with the crystal structure. Shown are two orientations of the surface of MCP CCP3-4 as in the crystal structure of the C3b-MCP complex, highlighting the contact sites with the C3b platform (purple), the MCP mutations identified as critical for C3b binding (red) and those not affecting the interaction (blue). The GB24 antibody epitope is shown as yellow contour on the MCP surface. 