Residues encoded by PSC in the three-dimensional structure of human IgA1 and their relationship to sites of biological interest.

<p>A, Model of human IgA1 (PBD ID 1iga) with residues encoded by PSC highlighted. The light chains are colored green and the heavy chains colored yellow. Positively selected positions are represented by red dots (selected in mammals), black dots (selected in primates and mammals) or blue dots (selected in primates). B to F, Human IgA1-Fc (PDB ID 1OW0) with residues critical for FcαRI interaction (B), pIgR interaction (C), SSL7 interaction (D), streptococci IgA binding proteins interaction (E), and <i>H. influenzae</i> type 2 IgA1 protease interaction (F) highlighted in cyan, orange, pink, purple and grey respectively. Positively selected positions are represented as in panel A. Differences between the Fc structures in A and B-F reflect the fact that the model of intact IgA1 in A is based on low resolution X-ray and neutron scattering modeled based on the X-ray crystal structure of IgG Fc (the closest structure available at the time of modeling), while B-F show an X-ray crystal structure of human IgA1-Fc solved as part of a complex with FcαRI (not shown).