D. Model of the putative positioning of the flexible CCP1-2 domains of MCP. The model has been generated by superposing the structure of CCP1-4 of MCP from PDB 3O8E (Persson et al, 2010) onto the structure of the C3b-MCP (CCP1-4) complex. CCP1-2 domains of MCP, not visible in the C3b-MCP (CCP1-4) structure, are shown in grey. 