The Na ⁺ -pumping mechanism driven by redox reactions in the NADH-quinone oxidoreductase from Vibrio cholerae relies on dynamic conformational changes

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Na⁺-NQR is a vital respiratory enzyme in bacteria.
• It couples electron transfer to Na⁺-pumping across membranes.
• Previous structures hinted at conformational changes during catalysis.

Purpose of the Study:

• To structurally characterize the conformational states of Na⁺-NQR.
• To elucidate the mechanism of Na⁺ translocation.
• To validate proposed catalytic rearrangements.

Main Methods:

• Utilized mutants lacking specific cofactors.
• Employed specific enzyme inhibitors.
• Investigated low-sodium conditions.
• Performed molecular dynamics simulations.

Main Results:

• Identified at least five distinct conformational states of Na⁺-NQR.
• 2Fe-2S reduction in NqrD/E is critical for Na⁺ translocation.
• This reduction drives rearrangements in NqrD/E, affecting NqrC and NqrF.
• Provided first structural insights into Na⁺-NQR's translocation mechanism.

Conclusions:

• Confirmed conformational changes in Na⁺-NQR during turnover.
• Elucidated the role of NqrD/E redox centers in triggering Na⁺ pumping.
• Established a structural basis for Na⁺ translocation coupled to electron transfer.