Recombinant Gorilla gorilla gorilla NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 4 (NDUFB4)

What is the function of NDUFB4 in mitochondrial respiration?

NDUFB4 is an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) that participates in electron transfer from NADH to the respiratory chain. While not directly involved in catalysis, NDUFB4 plays a crucial structural role in complex I assembly and stability . The immediate electron acceptor is believed to be ubiquinone .

Recent research has revealed that NDUFB4 contains specific residues (particularly Asn24 and Arg30) that interact with the UQCRC1 subunit from Complex III, making it integral for I₁III₂IV₁ "respirasome" supercomplex formation and integrity . These supercomplexes are essential for optimal mitochondrial function and cellular bioenergetics.

To study NDUFB4 function, researchers typically employ:

• Seahorse XF analysis to measure oxygen consumption rates

• Blue Native PAGE to visualize respiratory complex assembly

• Immunodetection methods with specific antibodies

• Site-directed mutagenesis to analyze key residues

How is NDUFB4 involved in respiratory supercomplex assembly?

NDUFB4 plays a critical role in the assembly and stability of respiratory supercomplexes (SCs), particularly the I₁III₂IV₁ "respirasome." Recent research has demonstrated that specific amino acid residues in NDUFB4 are essential for these structures.

Key findings from research:

• NDUFB4 contains residues (specifically Asn24 and Arg30) that directly interact with Complex III subunit UQCRC1

• Point mutations N24A and R30A in NDUFB4 impair I₁III₂IV₁ respirasome assembly

• NDUFB4 knockout cells exhibit significantly reduced oxygen consumption rates

• Reintroduction of wild-type NDUFB4 restores respiratory function, while mutant forms only partially rescue this phenotype

When studying supercomplex assembly, researchers should:

• Use Blue Native PAGE to visualize intact complexes

• Apply in-gel activity assays to assess functional assembly

• Implement crosslinking studies to identify precise interaction sites

• Conduct respiration measurements to confirm functional consequences

What expression systems work best for recombinant Gorilla gorilla gorilla NDUFB4?

For optimal expression of recombinant Gorilla gorilla gorilla NDUFB4, several expression systems can be employed, each with specific advantages:

• Bacterial systems (E. coli):

  • Advantages: High yield, cost-effective, rapid production

  • Limitations: Lack of post-translational modifications, potential misfolding of membrane proteins

  • Recommendation: Use specialized strains (C41/C43) designed for membrane protein expression

• Yeast systems (P. pastoris, S. cerevisiae):

  • Advantages: Post-translational modifications, proper folding of eukaryotic proteins

  • Limitations: Lower yield than bacterial systems, longer production time

  • Recommendation: Consider for structural studies requiring authentic folding

• Mammalian expression systems (HEK293, CHO):

  • Advantages: Most authentic processing and folding, proper post-translational modifications

  • Limitations: Higher cost, lower yield, complex maintenance

  • Recommendation: Optimal for functional studies and protein-protein interaction analyses

• Insect cell systems (Sf9, Hi5):

  • Advantages: Higher yield than mammalian systems with similar post-translational modifications

  • Limitations: More complex than bacterial systems, requires specialized equipment

  • Recommendation: Good compromise for structural studies requiring both yield and authenticity

For purification, incorporate a fusion tag (His-tag or GST) and implement detergent-based extraction methods suitable for membrane proteins. Consider adding stabilizing agents during purification to maintain the native conformation of this hydrophobic protein.

What antibody considerations are important for NDUFB4 detection?

When selecting antibodies for NDUFB4 detection, researchers should consider several factors based on application requirements and experimental design:

Important considerations:

• For antigen retrieval in IHC, TE buffer at pH 9.0 is recommended; alternatively, citrate buffer at pH 6.0 can be used

• When selecting antibodies, verify cross-reactivity with Gorilla gorilla gorilla NDUFB4 (high sequence conservation makes human-reactive antibodies potentially suitable)

• For co-localization studies, combine NDUFB4 antibodies with other mitochondrial markers

• Consider using recombinant monoclonal antibodies for higher specificity and reproducibility

• Always include proper controls, including knockout/knockdown samples when available

For Western blotting, the predicted molecular weight is 15 kDa, which matches the observed molecular weight in experimental conditions .

How can researchers measure NDUFB4's impact on cellular bioenergetics?

Assessing NDUFB4's influence on cellular bioenergetics requires comprehensive methodological approaches:

• Seahorse XF Analysis:

  • Measure key respiratory parameters including:

    • Basal respiration

    • ATP-linked respiration (calculated as the difference between basal and leak respiration)

    • Maximal respiration (induced by FCCP)

    • Spare respiratory capacity

    • Non-mitochondrial respiration (after antimycin A/rotenone addition)

• Complex-Specific Respiration Measurements:

  • Assess Complex I-specific OXPHOS using pyruvate/malate/glutamate substrates

  • Measure Complex II-specific OXPHOS using succinate as substrate (with rotenone)

  • Compare the ratio of CI/CII-linked respiration to detect metabolic shifts

• Metabolomic Analysis:

  • Implement steady-state metabolomics to analyze TCA cycle intermediates

  • Measure NADH/NAD+ ratios to assess electron transport chain function

  • Quantify ATP/ADP ratios to evaluate bioenergetic efficiency

Research findings show that NDUFB4 mutations significantly affect respiratory parameters:

• N24A and R30A mutations reduced resting OCR by 31%

• ATP-linked respiration decreased by 33% in mutant cells

• Complex I-specific respiration was particularly affected

• Cells showed increased reliance on Complex II-linked respiration as a compensatory mechanism

How does NDUFB4 function compare to NDUFS4 in respiratory complex assembly?

While both are accessory subunits of respiratory Complex I, NDUFB4 and NDUFS4 exhibit distinct functions in complex assembly and mitochondrial physiology:

Research findings demonstrate that NDUFS4 deficiency results in:

• Reduced attachment between N and Q modules

• Decreased steady-state levels of several core Complex I subunits

• Stabilization of NDUFAF2-containing assembly intermediates

• Accumulation of a partially assembled 830 kDa Complex I subcomplex

In contrast, NDUFB4 mutations primarily affect:

Understanding these distinctions is crucial when designing experimental approaches to study respective protein functions in respiratory chain organization.

What are the implications of NDUFB4 in cancer, particularly in gastric carcinoma?

Emerging evidence suggests important connections between NDUFB4 and cancer biology, particularly in gastric carcinoma. While direct research on NDUFB4 in cancer is limited, related mitochondrial complex I components show significant associations:

• Expression patterns:

  • NDUFB4 can be detected in human stomach cancer tissue using immunohistochemistry

  • The related complex I subunit NDUFS4 shows high expression in gastric cancer tissues

  • NDUFS4 high expression correlates with terminal TNM stage and unfavorable survival

• Clinical correlations:

  • NDUFS4 expression in gastric cancer correlates strongly with:

    • Diffuse type classification (χ² = 9.188, P = 0.010)

    • Poor differentiation (χ² = 23.628, P < 0.001)

    • Advanced T/N/M staging (all P < 0.001)

• Functional implications:

  • Downregulation of NDUFS4 decreases gastric cancer cell proliferation, migration, and invasion

  • NDUFS4 knockdown reduces tumor growth in nude mouse models

  • Mitochondrial complex I dysfunction affects cellular bioenergetics and potentially metastatic potential

• Research methodologies:

  • Use cancer tissue microarrays with immunohistochemistry to assess expression

  • Perform bioinformatics analyses to correlate expression with clinical parameters

  • Implement knockdown/knockout approaches to evaluate functional consequences

  • Monitor changes in cellular metabolism upon mitochondrial complex alteration

These findings collectively suggest that NDUFB4, as a critical component of mitochondrial complex I and respirasome formation, may play similar roles in cancer biology as observed with NDUFS4, potentially offering new therapeutic targets or prognostic markers.

How do point mutations in NDUFB4 affect mitochondrial metabolism beyond respiration?

Point mutations in NDUFB4, particularly at residues N24 and R30, have wide-ranging effects on mitochondrial metabolism that extend beyond direct impacts on respiration:

• Metabolic pathway alterations:

  • Global decrease in citric acid cycle metabolites

  • Shift from Complex I to Complex II-dependent respiration

  • Potential compensatory upregulation of glycolysis

  • Altered NADH/NAD+ ratios affecting numerous NAD-dependent enzymes

• Mitochondrial network changes:

  • Mutations potentially affect mitochondrial morphology and dynamics

  • Altered fusion/fission balance in response to bioenergetic stress

  • Potential impact on mitochondrial quality control mechanisms

  • Changes in mitochondrial membrane potential affecting transport processes

• Cellular adaptation mechanisms:

  • Activation of retrograde signaling pathways from mitochondria to nucleus

  • Altered expression of nuclear-encoded mitochondrial genes

  • Potential activation of mitochondrial unfolded protein response

  • Changes in calcium handling between mitochondria and endoplasmic reticulum

• Methodological approaches:

  • Implement steady-state metabolomics to quantify TCA cycle intermediates

  • Use isotope tracing to track metabolic flux through key pathways

  • Combine respirometry with metabolic profiling for integrated analysis

  • Apply live-cell imaging to monitor dynamic changes in mitochondrial networks

Research demonstrates that disruption of respirasome formation through NDUFB4 mutations leads to comprehensive metabolic reprogramming as cells adapt to altered electron transport chain function and efficiency.

What computational methods can assess evolutionary conservation of NDUFB4 across primate species?

Advanced computational approaches provide valuable insights into NDUFB4 evolutionary patterns across primates, including Gorilla gorilla gorilla:

• Sequence-based analyses:

  • Multiple sequence alignment using MUSCLE, MAFFT, or T-Coffee algorithms

  • Calculation of percent identity and similarity matrices

  • Identification of conserved domains using PFAM or CDD databases

  • Detection of species-specific insertions/deletions

• Phylogenetic methods:

  • Maximum likelihood tree construction (RAxML, PhyML)

  • Bayesian inference approaches (MrBayes, BEAST)

  • Ancestral sequence reconstruction to identify evolutionary trajectory

  • Tests for selection pressure using PAML or HyPhy

• Structural bioinformatics:

  • Homology modeling using templates from related species

  • Molecular dynamics simulations to assess functional conservation

  • Protein-protein interaction interface analysis

  • Identification of co-evolving residues within the protein

• Systems biology approaches:

  • Analysis of conserved protein-protein interactions

  • Comparative metabolic modeling across species

  • Evaluation of mitochondrial network conservation

  • Integration of expression data with sequence conservation

Key considerations for primate NDUFB4 analysis include examining residues critical for respirasome formation (particularly N24 and R30) and identifying whether selection pressure differs between great apes and other primates, potentially reflecting metabolic adaptations related to diet, body size, and activity patterns.

How can alternative splicing of NDUFB4 be studied in relation to mitochondrial function?

Alternative splicing (AS) represents an important regulatory mechanism that can significantly impact NDUFB4 function and mitochondrial physiology. Recent research has revealed AS events can affect mitochondrial components:

• Detection methodologies:

  • RNA-seq analysis with specialized splice junction detection algorithms

  • RT-PCR with primers spanning potential splice junctions

  • Minigene constructs to test specific splicing events

  • Northern blotting to detect isoform diversity

• Regulatory mechanisms:

  • Identification of RNA-binding proteins controlling NDUFB4 splicing

  • Analysis of splice site strength and branch point sequences

  • Evaluation of secondary structure influences on splicing

  • Assessment of epigenetic factors affecting alternative splicing

• Functional consequences:

  • Expression of splice variants in knockout cellular models

  • Analysis of protein stability and localization for different isoforms

  • Assessment of complex assembly efficiency with variant isoforms

  • Measurement of respiratory function with different splice variants

Recent research provides a relevant example: IQGAP1 knockout in gastric cancer cells altered the alternative splicing of NDUFS4 by increasing exon 2 skipping, which disrupted the reading frame and generated an NMD substrate . This led to:

• Downregulation of NDUFS4 transcript and protein levels

• Reduced complex I activity

• Accumulation of assembly intermediates resembling Leigh syndrome patterns

Similar mechanisms might affect NDUFB4 processing, potentially contributing to mitochondrial dysfunction in various physiological and pathological conditions. Investigating AS events in Gorilla gorilla gorilla NDUFB4 could reveal species-specific regulatory mechanisms affecting mitochondrial function.

What are the optimal protocols for measuring NDUFB4-dependent respiratory complex activity?

Measuring respiratory complex activity related to NDUFB4 function requires specialized techniques with careful attention to experimental conditions:

• Oxygen consumption measurements:

  • Utilize high-resolution respirometry (Oroboros Oxygraph-2k) or Seahorse XF analyzers

  • Isolate mitochondria using differential centrifugation with protease inhibitors

  • Implement substrate-uncoupler-inhibitor titration (SUIT) protocols:

    • Complex I-linked: Glutamate/Malate or Pyruvate/Malate

    • Complex II-linked: Succinate (with rotenone)

    • Combined pathways: Glutamate/Malate/Succinate

  • Measure in both coupled (ADP-stimulated) and uncoupled (FCCP) states

• Spectrophotometric assays:

  • For Complex I: NADH:ubiquinone oxidoreductase activity

    • Monitor NADH oxidation at 340 nm

    • Normalize to citrate synthase activity

    • Include rotenone-insensitive control measurements

  • For supercomplexes: Combined NADH-cytochrome c reductase activity

    • Measures integrated Complex I+III activity

    • Particularly relevant for NDUFB4 function assessment

• Complex assembly analysis:

  • Blue Native PAGE followed by:

    • In-gel activity assays (NADH:NBT reductase)

    • Western blotting for specific complex subunits

    • Second-dimension SDS-PAGE for subunit composition

• Controls and considerations:

  • Always include wild-type, knockout, and rescued samples

  • Consider temperature sensitivity (perform assays at physiological temperatures)

  • Account for tissue-specific differences in mitochondrial function

  • Maintain consistent substrate concentrations across experiments

Research has shown that N24A and R30A mutations in NDUFB4 reduced basal OCR by 31%, leak OCR by 24%, and maximal OCR by 40% compared to wild-type rescue cells , demonstrating the significant impact of NDUFB4 structure on respiratory function.

How can researchers design comparative studies between human and gorilla NDUFB4?

Designing robust comparative studies between human and Gorilla gorilla gorilla NDUFB4 requires careful methodological planning:

• Sequence and structure comparison:

  • Perform comprehensive sequence alignment and conservation analysis

  • Identify species-specific amino acid substitutions

  • Create homology models for both proteins

  • Apply molecular dynamics simulations to assess structural differences

• Expression system selection:

  • Use identical expression systems for both proteins

  • Consider mammalian cells with endogenous NDUFB4 knockout

  • Create chimeric proteins to identify functionally divergent domains

  • Evaluate expression level and stability differences

• Functional rescue experiments:

  • Generate NDUFB4-knockout cell lines

  • Express human or gorilla NDUFB4 in these cells

  • Measure:

    • Respiratory complex assembly (BN-PAGE)

    • Oxygen consumption rates (Seahorse XF or respirometry)

    • Supercomplex formation and stability

    • Mitochondrial membrane potential maintenance

• Protein-protein interaction comparisons:

  • Perform immunoprecipitation with species-specific or conserved binding partners

  • Use proximity labeling approaches (BioID, APEX)

  • Quantify interaction strengths through surface plasmon resonance

  • Identify differential interaction networks

• Evolutionary context analysis:

  • Relate functional differences to species-specific metabolic demands

  • Consider dietary adaptations (gorillas are primarily herbivorous)

  • Assess potential adaptation to different environmental conditions

  • Examine conservation patterns in interacting proteins

This comparative approach provides insights into both conserved functions and species-specific adaptations in mitochondrial respiratory chain organization, potentially revealing evolutionary mechanisms driving primate energy metabolism.

What are the technical challenges in generating NDUFB4 knockout models?

Creating NDUFB4 knockout models presents several technical challenges that researchers must carefully navigate:

• Cellular viability concerns:

  • Complete NDUFB4 knockout may severely compromise mitochondrial function

  • Cells might undergo metabolic reprogramming to compensate

  • Selection pressure may favor cells with incomplete knockout

  • Consider using inducible knockout systems to control timing

• CRISPR/Cas9 design considerations:

  • Design multiple guide RNAs targeting different exons

  • Verify specificity to avoid off-target effects

  • Consider potential alternative start sites

  • Implement strategies for homology-directed repair to insert selection markers

• Validation challenges:

  • Confirm knockout at DNA, RNA, and protein levels

  • Use antibodies with validated specificity

  • Implement functional assays to confirm mitochondrial consequences

  • Screen multiple clones to identify complete knockouts

• Species-specific considerations for Gorilla gorilla gorilla:

  • Limited availability of gorilla cell lines

  • Consider creating knockouts in human cells followed by gorilla NDUFB4 expression

  • Use gorilla-specific sequence information for guide RNA design

  • Validate antibody cross-reactivity between species

• Alternative approaches:

  • Consider knockdown approaches if knockout is lethal

  • Implement tissue-specific knockout in animal models

  • Use degradation systems (e.g., auxin-inducible degron) for temporal control

  • Create hypomorphic alleles rather than complete knockouts

Research has demonstrated successful NDUFB4 knockout in certain cell lines, with significant consequences for respiratory function , but researchers must carefully optimize protocols for specific experimental systems and research questions.

How can mass spectrometry be optimized for NDUFB4 detection and characterization?

Mass spectrometry (MS) offers powerful approaches for NDUFB4 detection and characterization, but requires careful optimization:

• Sample preparation optimization:

  • Implement detergent-based extraction methods suitable for hydrophobic membrane proteins

  • Consider filter-aided sample preparation (FASP) for detergent removal

  • Test multiple proteases beyond trypsin (e.g., chymotrypsin, Glu-C) to increase sequence coverage

  • Use mitochondrial enrichment through differential centrifugation

• Peptide detection strategies:

  • Develop multiple reaction monitoring (MRM) assays for NDUFB4-specific peptides

  • Create spectral libraries from recombinant protein

  • Implement parallel reaction monitoring (PRM) for improved specificity

  • Consider data-independent acquisition (DIA) for comprehensive analysis

• Post-translational modification analysis:

  • Apply enrichment strategies for phosphopeptides (TiO2, IMAC)

  • Use electron transfer dissociation (ETD) for improved PTM site localization

  • Implement quantitative strategies to assess modification stoichiometry

  • Consider top-down approaches for intact protein analysis

• Protein-protein interaction studies:

  • Combine immunoprecipitation with MS (IP-MS)

  • Apply crosslinking mass spectrometry (XL-MS) to identify interaction interfaces

  • Consider hydrogen-deuterium exchange MS to detect conformational changes

  • Implement proximity labeling approaches (BioID, APEX) followed by MS

• Data analysis considerations:

  • Use specialized search engines for membrane proteins

  • Implement targeted approaches for low-abundance peptides

  • Apply ion mobility separation for improved peptide detection

  • Consider de novo sequencing for novel or modified peptides

The "Mass-spec analysis" tool described in search result provides a platform to analyze and store mass spectrometric data, generating LFC/LogP volcano plots, performing pathway analyses, and facilitating dataset comparisons, which can be valuable for NDUFB4 research.

What complementary techniques should accompany respirometry in NDUFB4 studies?

While respirometry provides crucial functional data, comprehensive NDUFB4 characterization requires integration with complementary techniques:

• Structural analysis techniques:

  • Blue Native PAGE to assess respiratory complex assembly

  • Clear Native PAGE with in-gel activity assays

  • Western blotting for NDUFB4 and interacting proteins

  • Immunoprecipitation to identify binding partners

• Imaging methodologies:

  • Confocal microscopy to assess mitochondrial morphology

  • Super-resolution techniques (STED, STORM) for detailed structural analysis

  • Live-cell imaging with mitochondrial function indicators

  • Transmission electron microscopy for ultrastructural assessment

• Molecular biology approaches:

  • RT-qPCR for gene expression analysis

  • RNA-seq to assess transcriptome-wide effects

  • Alternative splicing analysis through specialized PCR approaches

  • CRISPR-based genetic manipulation to create model systems

• Metabolic profiling:

  • Steady-state metabolomics of TCA cycle intermediates

  • Flux analysis using isotope-labeled substrates

  • ATP/ADP and NADH/NAD+ ratio measurements

  • Lactate production as indicator of glycolytic compensation

• ROS and mitochondrial function assessments:

  • Mitochondrial membrane potential measurements

  • ROS detection using specific fluorescent probes

  • Mitochondrial calcium uptake assays

  • Cell viability and proliferation assessments

Integration of these complementary approaches provides a comprehensive understanding of how NDUFB4 contributes to mitochondrial function beyond respiratory measurements alone. Research has demonstrated that mutations in respiratory complex assembly proteins like NDUFB4 have multifaceted effects on cellular physiology that cannot be captured by single methodological approaches .