Structural elucidation of the haptoglobin–hemoglobin clearance mechanism by macrophage scavenger receptor CD163
Fig 3
Ubiquitous Ca+2-mediated electrostatic interactions in the structure of the CD163/Hp(1–1)Hb complex.
(A) Surface representation of the CD163/Hp(1–1)Hb structure colored by each component. CD163 SRCR domains (D2–D9) are labeled on the surface. (B–F) Close-up views of the interactions between the CD163 trimer and HpHb protomer (B–E) and the interactions between CD163-I D9 and CD163-II D7 (F). The key residues and Ca+2 ions involved in these interactions are shown as sticks and spheres, respectively. Magenta dashed lines indicate salt bridges between Lys/Arg and Asp/Glu residues. Yellow dashed lines indicate hydrogen bonds. The cryo-EM map in these regions is shown as gray surface. (G) SEC-MALS analysis of CD163/Hp(1–1)Hb with and without adding EDTA. (H) Mass photometry analysis of 50 nM of CD163/Hp(1–1)Hb with and without adding EDTA. Source data for (G–H) can be found in S1 Data.