Structural elucidation of the haptoglobin–hemoglobin clearance mechanism by macrophage scavenger receptor CD163
Fig 4
Structural comparison between the unliganded and Hp(1–1)Hb bound CD163 trimer.
(A) Structure Superposition of the unliganded and Hp(1–1)Hb bound CD163 trimer based on the alignment of D6 to D8 from CD163-I (RMSD = 0.81 Å) to inspect structural motions of CD163 subunits for Hp(1–1)/Hb binding. (B) Focused view on CD163-I showing that its D2 to D5 rotates 20o and shifts 11 Å with additional horizontal 73o rotation of the D2, and its D9 rotates 30o and shifts 8 Å. (C) Focused view on CD163-II showing that it rotates 47o and shifts 52 Å, accompanying the movement of CD163-I D9 and preserving the Ca+2-medicated D7–D9 interactions between CD163-I and CD163-II. (D) Focused view on CD163-III showing that its D3 to D8 rotates 28o and shifts 12 Å to establish the Ca+2-medicated D7–D9 interactions between CD163-II and CD163-III. At the same time, CD163-III D9 slightly rotates 3o and shits 4 Å, preserving the Ca+2-medicated D7–D9 interactions between CD163-I and CD163-III. (E) bottom view of the CD163 trimers showing that D9 of CD163-II connects with D7 of CD163-III to form an enclosed structure upon Hp(1–1)Hb binding. Each CD163 subunit is colored as in (A–D). Hp(1–1)Hb is shown as surface and colored as in Fig 3.