Recombinant Escherichia coli NADH-quinone oxidoreductase subunit K (nuoK)
Description
Introduction to Recombinant Escherichia coli NADH-Quinone Oxidoreductase Subunit K (nuoK)
Recombinant E. coli NADH-quinone oxidoreductase subunit K (nuoK) is a hydrophobic subunit of the bacterial proton-translocating NADH-quinone oxidoreductase (NDH-1), a respiratory enzyme homologous to mitochondrial complex I. NuoK is the smallest subunit of NDH-1, spanning three transmembrane segments (TM1–3) and playing a critical role in coupling electron transfer to proton translocation across the cytoplasmic membrane . Its structure and function are conserved in eukaryotic ND4L subunits, making it a key model for studying complex I mechanisms in mitochondrial diseases .
Membrane Topology and Subunit Interactions
NuoK forms a linear arrangement of three α-helices connected by short loops, interacting extensively with NuoN (ND2 homolog) and NuoL (ND5 homolog) . Its cytoplasmic loop-1 (residues 25–27) contains conserved arginines (Arg-25, Arg-26) critical for proton translocation .
Table 1: Impact of NuoK Mutations on NDH-1 Activity
| Mutation | Electron Transfer Activity (%) | Proton Translocation (%) | Source |
|---|---|---|---|
| KGlu-36 → Ala | 0 | 0 | |
| KGlu-72 → Ala | ~50 | ~40 | |
| R25A/R26A (loop-1) | ~20 | ~10 |
Flexibility in Proton Channel Architecture
Repositioning KGlu-36 along TM2 (e.g., to positions 32, 38, 39, or 40) preserves NDH-1 activity, indicating structural flexibility in proton channel formation . This contrasts with rigid requirements for conserved residues like MGlu-144 in NuoM .
Assembly and Stability
NuoK mutants (e.g., KGlu-36 → Ala) assemble into NDH-1 but fail to generate membrane potential. Membrane vesicles with mutant nuoK show:
Role of Cytoplasmic Loop-1
Mutations in Arg-25/Arg-26 disrupt electrochemical gradient formation but not electron transfer, suggesting these residues stabilize proton channel dynamics .
Modeling Human Complex I Mutations
E. coli nuoK mutants serve as proxies for studying mitochondrial ND4L mutations. For example:
-
KGlu-72 → Ala: Mimics defects in proton translocation linked to mitochondrial diseases .
-
R25A/R26A: Explored for insights into proton channel gating mechanisms .
Mechanistic Hypotheses
NuoK’s Glu residues may:
Product Specs
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Important note: All protein shipments are standardly sent with blue ice packs. If you require dry ice shipping, please inform us in advance as an additional fee will apply.
Generally, the shelf life for liquid form is 6 months at -20°C/-80°C. The shelf life for lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: ecy:ECSE_2536
