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spinqualitylabelsall models 1nu1, resolution 3.20Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of Mitochondrial Cytochrome bc1 Complexed with 2-nonyl-4-hydroxyquinoline N-oxide (NQNO)

Overview

Cytochrome bc(1) is an integral membrane protein complex essential to, cellular respiration and photosynthesis. The Q cycle reaction mechanism of, bc(1) postulates a separated quinone reduction (Q(i)) and quinol oxidation, (Q(o)) site. In a complete catalytic cycle, a quinone molecule at the Q(i), site receives two electrons from the b(H) heme and two protons from the, negative side of the membrane; this process is specifically inhibited by, antimycin A and NQNO. The structures of bovine mitochondrial bc(1) in the, presence or absence of bound substrate ubiquinone and with either the, bound antimycin A(1) or NQNO were determined and refined. A ubiquinone, with its first two isoprenoid repeats and an antimycin A(1) were, identified in the Q(i) pocket of the substrate and inhibitor bound, structures, respectively; the NQNO, on the other hand, was identified in, both Q(i) and Q(o) pockets in the inhibitor complex. The two inhibitors, occupied different portions of the Q(i) pocket and competed with substrate, for binding. In the Q(o) pocket, the NQNO behaves similarly to, stigmatellin, inducing an iron-sulfur protein conformational arrest., Extensive binding interactions and conformational adjustments of residues, lining the Q(i) pocket provide a structural basis for the high affinity, binding of antimycin A and for phenotypes of inhibitor resistance. A, two-water-mediated ubiquinone protonation mechanism is proposed involving, three Q(i) site residues His(201), Lys(227), and Asp(228).

About this Structure

1NU1 is a Protein complex structure of sequences from Bos taurus with HEM, FES and QNO as ligands. Active as Ubiquinol--cytochrome-c reductase, with EC number 1.10.2.2 Full crystallographic information is available from OCA.

Reference

Structural basis for the quinone reduction in the bc1 complex: a comparative analysis of crystal structures of mitochondrial cytochrome bc1 with bound substrate and inhibitors at the Qi site., Gao X, Wen X, Esser L, Quinn B, Yu L, Yu CA, Xia D, Biochemistry. 2003 Aug 5;42(30):9067-80. PMID:12885240

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