Fig. 4.

UQ8 and key residues. (A) The UQ8 resides close to R71^I, D75^I, H98^I, and Q101^I. The distance between the UQ8 headgroup and heme b is ∼14 Å (center to center). (B) In the SMA-purified enzyme, H98^I has two conformations. The UQ8 is hydrogen bonded with R71^I, D75^I, and H98^I (“conformation 1”, Nε). Q101^I is 6.5 Å from O4 of UQ8. H98^I (“conformation 2”, Nε) is hydrogen bonded with E14^I. (C) In the MSP nanodisc structure, the UQ8 is hydrogen bonded with R71^I, D75^I, and H98^I (“conformation 1”, Nε). Q101^I is 7.2 Å from O4 of UQ8. H98^I (“conformation 2”, Nε) is 4.0 Å from E14^I.