Insights into the inhibitory mechanisms of NADH on the αγ heterodimer of human NAD-dependent isocitrate dehydrogenase.
Level 5 - mechanism / opinion, no new human data
In vitro structural biology and biochemical mechanism study (CEBM Level 5).
PubMed 29453450 · doi:10.1038/s41598-018-21584-7
What was done
The authors investigated the inhibitory mechanisms of NADH on recombinant forms of human NAD-dependent isocitrate dehydrogenase (NAD-IDH), including alpha-beta, alpha-gamma, and alpha2-beta-gamma complexes. They solved the crystal structure of the alpha-gamma heterodimer bound to Mg2+ and NADH and evaluated competitive biochemical binding against cofactors and allosteric activators.
What was found
NADH inhibited alpha-beta, alpha-gamma, and alpha2-beta-gamma complexes of human NAD-IDH. Crystal structure analysis revealed that one NADH molecule binds to the active site and blocks NAD+ binding, while a second NADH molecule binds to the allosteric site and blocks the binding of activators ADP and citrate. Biochemical assays confirmed that competitive binding at both sites mediates inhibition. No numerical values (e.g., Ki, IC50, or resolution metrics) were reported in the abstract.
Why it matters
This study defines the structural mechanism of feedback inhibition in human NAD-IDH, demonstrating how NADH simultaneously acts as a competitive inhibitor at the active site and a competitive antagonist at the allosteric activation site.
Limits
The study is entirely in vitro, structural data are focused on the alpha-gamma heterodimer rather than the full heterotetramer, and no in vivo or cellular validation was conducted. The abstract provides no quantitative kinetic parameters or crystallographic metrics.
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