Schematic representations of human α-macroglobulin (α₂M), C3 convertase (C3), and <i>E. coli</i> α-macroglobulin (ECAM).

<p>Domain assignments for α₂M and C3 were based on their respective crystal structures <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035384#pone.0035384-Marrero1" target="_blank">[13]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035384#pone.0035384-Janssen1" target="_blank">[17]</a>. Assignments for ECAM were performed with the JPRED server, supported by the analysis performed by Doan and Gettins <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035384#pone.0035384-Doan1" target="_blank">[27]</a>. 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 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035384#pone.0035384.s006" target="_blank">Fig. S6</a>).