|
Figure 7.
Figure 7 Putative proton uptake pathways at the Q[i] site of
yeast QCR via two arrays of hydrogen-bonded water molecules,
which connect the bulk solvent at the matrix side with the site
of ubiquinone reduction. The entrance to the E/R pathway is
formed by Glu52 of QCR7 and Wat176. The gating residue towards
the quinone-binding pocket is Arg218 of COB. Cardiolipin (L5) is
positioned at the entrance to the CL/K pathway, for which Lys228
of COB is the gating residue. Arrows indicate the access sites
from the bulk solvent, and double arrows show proton transfer
between the key residues Arg218 or Lys228 of COB and UQ6. Side
chains of amino acid residues that are involved in hydrogen bond
interactions or ion pair formation are shown (standard colors).
Dashed lines indicate hydrogen bond interactions. Dotted lines
are used for hydrogen bond interactions of UQ6 and CL ligands
(His202, Asp229 and Tyr28 of COB, and Lys288 and Lys289 of
CYT1). Water molecules in the cavity above the cardiolipin
headgroup are stabilized by interactions with side chains of
Lys228 of COB, Lys296 of CYT1 and His85 of QCR7. A surrounding
layer of non-polar residues (not shown) encloses the
water-filled cavity. Transmembrane helices are shown as ribbon
presentation and other polypeptide backbones as rope
presentation. UQ6, heme b[H] and CL are represented as stick
models.
|
