Figure 1. Schematic representations of human α-macroglobulin (α₂M), C3 convertase (C3), and E. coli α-macroglobulin (ECAM).

Domain assignments for α₂M and C3 were based on their respective crystal structures [13], [17]. Assignments for ECAM were performed with the JPRED server, supported by the analysis performed by Doan and Gettins [27]. Note the similarity in domain predictions, including MG and TED domains. The CLEQ sequence, a signature of the thioester bond, is present in all proteins. For simplicity, only a limited number of the domains identified or predicted for the different molecules are depicted, and only one monomer of α₂M is shown. The C-terminus of ECAM displays low sequence similarity to that of C3 (Fig. S6).