Recombinant Pongo pygmaeus NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 4 (NDUFB4)

What is NDUFB4 and what is its role in mitochondrial function?

NDUFB4 (NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 4) is a non-catalytic accessory subunit of mitochondrial Complex I (NADH:ubiquinone oxidoreductase), which is the first and largest enzyme complex in the mitochondrial electron transport chain. Although NDUFB4 does not directly participate in the catalytic activity of Complex I, it plays crucial structural roles:

• Forms part of the hydrophobic transmembrane region of Complex I

• Has an N-terminal domain that folds into an α-helix spanning the inner mitochondrial membrane

• Features a C-terminal hydrophilic domain that interacts with globular subunits of Complex I

• Contributes to the stability and assembly of the respiratory chain complexes

• Participates in the formation of respiratory supercomplexes (SCs)

The highly conserved two-domain structure suggests that NDUFB4 functions as an anchor for the NADH dehydrogenase complex at the inner mitochondrial membrane, which is critical for maintaining proper respiratory chain organization and function .

What are the recommended storage and handling conditions for recombinant Pongo pygmaeus NDUFB4?

Based on manufacturer recommendations for recombinant NDUFB4 proteins, the following storage and handling guidelines should be followed:

Storage Conditions:

• Short-term (up to one week): 4°C for working aliquots

• Long-term storage: -20°C, or preferably -80°C for extended periods

• Storage buffer typically consists of Tris-based buffer with 50% glycerol, optimized for protein stability

Handling Guidelines:

• Avoid repeated freeze-thaw cycles as they can compromise protein integrity

• Briefly centrifuge vials before opening to bring contents to the bottom

• Reconstitute lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol (5-50% final concentration) to aliquots for long-term storage

Stability Information:

• Liquid form: approximately 6 months at -20°C/-80°C

• Lyophilized form: approximately 12 months at -20°C/-80°C

Following these recommendations will help maintain the structural integrity and functional activity of the recombinant protein for experimental applications.

How is recombinant Pongo pygmaeus NDUFB4 typically produced?

Recombinant NDUFB4 from Pongo pygmaeus can be produced using various expression systems. Based on the available information:

Expression Systems:

• Bacterial (E. coli) expression systems (similar to that used for chicken NDUFB4)

• Baculovirus expression systems (as used for other Pongo pygmaeus mitochondrial proteins)

Production Process:

• Gene synthesis or cloning of the NDUFB4 sequence into appropriate expression vectors

• Addition of affinity tags (commonly His-tag) to facilitate purification

• Expression in the selected host system under optimized conditions

• Cell lysis and extraction of the target protein

• Purification using affinity chromatography

• Quality control assessment via SDS-PAGE (typical purity standards >85-90%)

Protein Characteristics:

• Tag information: The tag type may be determined during the production process, with His-tags being common

• Expression region: Full-length protein or specified regions (e.g., amino acids 2-129 as mentioned for some recombinant products)

• Quantification: Typically supplied in the range of 50 μg

The choice of expression system depends on research requirements, with each system offering different advantages regarding post-translational modifications, protein folding, and yield.

What methods can be used to assess the functional integrity of recombinant NDUFB4?

Several complementary approaches can be employed to evaluate the functional integrity of recombinant NDUFB4:

Biochemical Assessment:

• SDS-PAGE analysis to confirm proper molecular weight and purity

• Western blotting with antibodies specific to NDUFB4 or epitope tags

• Circular dichroism spectroscopy to assess secondary structure integrity

• Limited proteolysis to evaluate proper folding

Functional Integration Analysis:

• Blue-native PAGE (BN-PAGE) of digitonin-solubilized membrane proteins to assess incorporation into Complex I and supercomplexes

• Immunoprecipitation studies to confirm interactions with other Complex I subunits

• In vitro reconstitution with other Complex I components to assess assembly competence

Activity-Based Assays:

• Complex I activity measurement through NADH oxidase activity assays

• Oxygen consumption measurements in reconstituted systems

• Assessment of membrane insertion using liposome incorporation studies

Cell-Based Functional Rescue:

• Complementation studies in NDUFB4-deficient cell lines (similar to the experimental approach in search result #10)

• Measurement of cellular respiration parameters following introduction of recombinant NDUFB4

Structural Analysis:

• Hydrogen/deuterium exchange mass spectrometry to assess protein folding and dynamics

• Thermal shift assays to evaluate protein stability

A combination of these methods provides comprehensive information about the structural integrity and functional capacity of recombinant NDUFB4 proteins.

How does NDUFB4 contribute to respiratory supercomplex assembly?

Recent research has revealed NDUFB4's critical role in respiratory supercomplex formation, particularly in the assembly of the I₁III₂IV₁ "respirasome":

Key Structural Interactions:

• NDUFB4 contains specific residues on its N-terminus (particularly Asn24 and Arg30) that form salt-bridging interactions with residues in the highly conserved loop (Y257-T266) of subunit UQCRC1 from Complex III

• These interactions serve as molecular bridges between Complex I and Complex III

Experimental Evidence:

• Knock-out of NDUFB4 (B4-KO cells) results in complete loss of respiratory supercomplexes containing CI, CIII, and CIV

• Reintroduction of wild-type NDUFB4 restores supercomplex assembly

• Point mutations (N24A and R30A) in NDUFB4 significantly impair I₁III₂IV₁ respirasome assembly while minimally affecting Complex I assembly itself

Functional Significance:

• NDUFB4-mediated supercomplex formation appears crucial for optimal mitochondrial respiratory function

• Disruption of these interactions leads to reduced cellular respiratory capacity and metabolic alterations

This research highlights NDUFB4's role as more than just a structural component of Complex I, but as a critical mediator of higher-order organization of the respiratory chain, directly influencing mitochondrial bioenergetics and cellular metabolism.

How can Pongo pygmaeus NDUFB4 be used as a research tool for studying mitochondrial function?

Recombinant Pongo pygmaeus NDUFB4 offers several valuable applications for mitochondrial research:

Evolutionary and Comparative Studies:

• Investigation of primate-specific adaptations in mitochondrial function

• Comparative analyses with human NDUFB4 to identify conserved functional domains

• Study of positive selection in mitochondrial proteins across species

Structural Biology Applications:

• Contribution to Complex I structure determination

• Analysis of species-specific variations in supercomplex assembly

• Investigation of protein-protein interactions within the respiratory chain

Functional Reconstitution:

• In vitro reconstitution of respiratory complexes to study assembly mechanisms

• Cross-species compatibility studies of mitochondrial complex components

• Development of minimal functional systems for bioenergetic studies

Disease Modeling:

• Comparative studies with human disease-associated NDUFB4 variants

• Investigation of evolutionary adaptations that might confer resistance to mitochondrial dysfunction

• Development of therapeutic approaches based on conserved functional mechanisms

Methodological Research Controls:

• Positive control for antibody specificity testing

• Standard for mass spectrometry-based proteomic studies

• Reference material for developing mitochondrial protein isolation techniques

The high degree of conservation between Pongo pygmaeus and human NDUFB4, combined with the species-specific adaptations, makes this protein a valuable tool for understanding both fundamental aspects of mitochondrial function and its role in human disease.

What experimental approaches can be used to study NDUFB4's role in respiratory supercomplex formation?

Several complementary experimental approaches can be employed to investigate NDUFB4's specific role in respiratory supercomplex formation:

Genetic Manipulation Approaches:

• CRISPR/Cas9-mediated knockout of NDUFB4 (as described in search results)

• Rescue experiments with wild-type and mutant NDUFB4 variants

• Site-directed mutagenesis of specific residues (particularly Asn24 and Arg30) identified as crucial for interactions with Complex III

Structural Analysis:

• Cryo-electron microscopy of intact supercomplexes with wild-type or mutant NDUFB4

• Cross-linking mass spectrometry to identify interaction partners

• Molecular modeling and simulations to predict interaction interfaces

Biochemical Characterization:

• Blue-native PAGE (BN-PAGE) with immunoblotting to visualize supercomplex assembly

• Co-immunoprecipitation studies to identify interaction partners

• In vitro reconstitution of supercomplexes using purified components

Functional Assessment:

• Respirometry to measure oxygen consumption in cells with wild-type vs. mutant NDUFB4

• Complex-specific substrate oxidation measurements

• Reactive oxygen species production assessment

Metabolic Analysis:

• Steady-state metabolomics to analyze changes in metabolite levels (particularly citric acid cycle intermediates)

• Metabolic flux analysis using isotope-labeled substrates

• Assessment of NAD+/NADH ratios in cells with altered NDUFB4 function

These approaches, particularly when used in combination, can provide comprehensive insights into how NDUFB4 contributes to the formation, stability, and function of respiratory supercomplexes.

How do specific mutations in NDUFB4 affect mitochondrial bioenergetics and cellular metabolism?

Recent research has elucidated how specific mutations in NDUFB4 influence mitochondrial function and cellular metabolism:

Effects on Supercomplex Assembly:

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

• These mutations specifically affect residues that form interactions with Complex III (UQCRC1 subunit)

• Importantly, these mutations minimally impact Complex I assembly itself, allowing isolation of supercomplex-specific effects

Impact on Mitochondrial Respiration:

Metabolic Adaptations:

• Shift from Complex I-dependent to Complex II-dependent respiration:

  • Reduced CI-specific OXPHOS

  • Increased CII-specific OXPHOS

• This represents a metabolic adaptation to compensate for impaired Complex I function

Effects on Metabolite Levels:

• Global decrease in citric acid cycle metabolites

• Particularly affected are NADH-generating substrates

• This indicates widespread metabolic reprogramming as a consequence of disrupted supercomplex formation

These findings demonstrate that NDUFB4-mediated supercomplex formation is not merely a structural phenomenon but has profound functional implications for cellular bioenergetics and metabolism, highlighting the importance of respiratory chain organization for optimal mitochondrial function.

What is the evolutionary significance of NDUFB4 conservation and adaptation across species?

The evolutionary patterns of NDUFB4 provide insights into its functional importance and species-specific adaptations:

Evidence of Conservation:

• NDUFB4's core structure and function are highly conserved across mammals, indicating fundamental importance to mitochondrial function

• The two-domain structure (N-terminal hydrophobic domain and C-terminal hydrophilic domain) is maintained across species, suggesting crucial functional significance

Adaptive Selection:

• Search results indicate "adaptive changes were seen in the NDUFB4 (B15) subunit" across species including Pongo pygmaeus

• Evidence of positive selection was found at specific evolutionary timepoints:

  • Preceding the emergence of apes

  • Following the emergence of orangutans

Functional Implications:

• Adaptation in NDUFB4 may reflect species-specific metabolic requirements

• Changes might be associated with adaptation to different ecological niches, dietary patterns, or energy demands

• The timing of positive selection suggests potential roles in primate evolution and adaptation

Comparative Biology Applications:

• Study of NDUFB4 from different species can provide insights into how mitochondrial function has evolved

• Identification of conserved vs. variable regions helps pinpoint functionally critical domains

• Understanding species-specific adaptations may inform research on human mitochondrial diseases

This evolutionary perspective on NDUFB4 highlights how structural modifications of respiratory chain components may have contributed to metabolic adaptations during mammalian evolution, particularly in primates, while maintaining core functionality essential for cellular energy production.

How does NDUFB4 interact with other components of the respiratory chain to regulate mitochondrial function?

NDUFB4 engages in specific interactions with components of both Complex I and Complex III to influence respiratory chain organization and function:

Interactions within Complex I:

• Located in the transmembrane region of Complex I, NDUFB4 likely interacts with adjacent membrane-embedded subunits

• Contributes to the structural integrity of the complex through its hydrophobic and hydrophilic domains

• May participate in the assembly pathway of Complex I

Interactions with Complex III:

• Forms critical interactions with Complex III through specific residues on its N-terminus

• Asn24 and Arg30 residues of NDUFB4 interact with the conserved loop (Y257-T266) of UQCRC1 from Complex III

• These interactions are essential for I₁III₂IV₁ respirasome formation

Functional Consequences of Interactions:

• Facilitates efficient electron transfer between Complex I and Complex III

• Contributes to the stability of respiratory supercomplexes

• Influences the organization of the inner mitochondrial membrane

• Affects the distribution of ubiquinone/ubiquinol between complexes

Regulatory Implications:

• NDUFB4-mediated interactions may serve as regulatory points for respiratory chain function

• The stability of these interactions could be modulated by metabolic conditions or cellular signaling

• Disruption of these interactions leads to metabolic reprogramming, suggesting their importance in maintaining optimal mitochondrial function

Understanding these interactions provides insights into how the structural organization of the respiratory chain influences its functional properties and how perturbations in this organization can lead to altered mitochondrial function and cellular metabolism.

What is the potential role of NDUFB4 in mitochondrial disease pathology?

While the search results don't provide direct evidence linking NDUFB4 mutations to specific human diseases, its critical role in respiratory chain function suggests potential involvement in mitochondrial disorders:

Potential Disease Mechanisms:

• Disruption of respiratory supercomplex assembly, as demonstrated with N24A and R30A mutations

• Impaired cellular respiration and ATP production

• Metabolic reprogramming and altered substrate utilization

• Potential increase in reactive oxygen species production

Relevant Disease Contexts:

• Mitochondrial Disorders:

  • Given NDUFB4's role in Complex I and supercomplex assembly, mutations could potentially contribute to Complex I deficiency syndromes

  • The bioenergetic deficits observed with NDUFB4 mutations mirror those seen in mitochondrial diseases

• Metabolic Diseases:

  • Search result #4 shows that another Complex I subunit (NDUFS4) is involved in diabetic kidney disease

  • Similar mechanisms might apply to NDUFB4, particularly given its impact on metabolic pathways

• Neurodegenerative Diseases:

  • Search result #13 mentions neurodegeneration as one of the diseases where supercomplex formation insights could be valuable

  • The high energy demands of neural tissues make them particularly vulnerable to mitochondrial dysfunction

• Cancer:

  • Search result #3 indicates that the Complex I subunit NDUFS4 promotes tumor progression in gastric cancer

  • Given the metabolic reprogramming observed with NDUFB4 mutations, similar oncogenic or tumor-suppressive roles might exist

Diagnostic Implications:

• Assessment of NDUFB4 expression or mutations could potentially serve as biomarkers for mitochondrial dysfunction

• Evaluation of supercomplex assembly might provide insights into disease mechanisms

These potential connections highlight the importance of further investigating NDUFB4's role in various disease contexts, particularly those involving mitochondrial dysfunction and metabolic alterations.

What methodologies can be used to study protein-protein interactions involving NDUFB4 in respiratory supercomplexes?

Several sophisticated methodologies can be employed to study NDUFB4's interactions within respiratory supercomplexes:

Structural Approaches:

• Cryo-electron microscopy (Cryo-EM): Provides high-resolution structural information about NDUFB4's position and interactions within intact supercomplexes

• Cross-linking mass spectrometry: Identifies proximity relationships between NDUFB4 and other subunits

• Hydrogen-deuterium exchange mass spectrometry: Maps interaction interfaces by detecting protected regions

Biochemical Methods:

• Blue-native PAGE: Preserves native protein complexes for visualization of intact supercomplexes

• Complexome profiling: Combines native electrophoresis with mass spectrometry to identify components of protein complexes

• Co-immunoprecipitation: Isolates NDUFB4 along with interacting partners

• Chemical cross-linking: Stabilizes transient interactions for subsequent analysis

Genetic and Functional Approaches:

• Site-directed mutagenesis: As demonstrated with N24A and R30A mutations, targeted mutations can reveal functionally important interaction sites

• CRISPR/Cas9 editing: Generate specific mutations or deletions to assess functional consequences

• Protein complementation assays: Split reporter systems that produce signal when proteins interact

Advanced Imaging Techniques:

• Förster resonance energy transfer (FRET): Detects proximity between fluorescently labeled proteins

• Super-resolution microscopy: Visualizes protein complexes beyond the diffraction limit

• Single-particle tracking: Follows the dynamics of complex formation

Computational Methods:

• Molecular dynamics simulations: Models the dynamic nature of protein-protein interactions

• Protein docking: Predicts potential interaction interfaces

• Evolutionary coupling analysis: Identifies co-evolving residues that may indicate interaction interfaces

The combination of these complementary approaches can provide comprehensive insights into how NDUFB4 interacts with other components of the respiratory chain to facilitate supercomplex formation and influence mitochondrial function.

How might recombinant NDUFB4 be used in the development of therapeutic approaches for mitochondrial disorders?

Recombinant NDUFB4 could contribute to therapeutic strategies for mitochondrial disorders in several ways:

Therapeutic Target Identification:

• Structure-function studies using recombinant NDUFB4 can identify critical domains for supercomplex assembly

• Screening platforms using recombinant protein to identify compounds that stabilize protein-protein interactions

• Development of peptide mimetics based on key interaction regions to enhance supercomplex stability

Gene and Protein Replacement Strategies:

• Recombinant NDUFB4 can serve as a reference for developing gene therapy approaches

• Optimization of protein delivery methods using recombinant NDUFB4 as a test substrate

• Development of stabilized NDUFB4 variants resistant to degradation or with enhanced assembly properties

Drug Discovery Applications:

• High-throughput screening systems using recombinant NDUFB4 to identify compounds that:

  • Enhance supercomplex assembly

  • Stabilize NDUFB4 structure

  • Promote NDUFB4 incorporation into Complex I

• Structure-based drug design targeting specific domains of NDUFB4

Disease Modeling and Personalized Medicine:

• Comparison of patient-specific NDUFB4 variants with wild-type recombinant protein

• Functional testing of therapeutic candidates using cellular models with recombinant NDUFB4 variants

• Development of assays to predict patient response to mitochondrial therapeutics

Biomarker Development:

• Generation of high-quality antibodies using recombinant NDUFB4 as immunogen

• Development of assays to measure NDUFB4 levels or modification states in patient samples

• Correlation of NDUFB4 status with disease progression or therapeutic response

While direct therapeutic applications are still emerging, the fundamental understanding gained through research with recombinant NDUFB4 provides crucial insights that may guide future development of targeted interventions for mitochondrial disorders.

What are the latest research developments regarding NDUFB4's role in respiratory chain organization and function?

Recent research has significantly advanced our understanding of NDUFB4's critical role in respiratory chain organization and function:

Key Recent Findings:

• Supercomplex Assembly Mechanism:

  • Identification of specific residues (Asn24 and Arg30) on NDUFB4 that form salt-bridging interactions with the UQCRC1 subunit of Complex III

  • These interactions are essential for I₁III₂IV₁ respirasome integrity

  • Point mutations (N24A and R30A) in these residues impair supercomplex assembly while minimally affecting Complex I assembly

• Functional Significance of Supercomplex Formation:

  • NDUFB4-mediated supercomplex formation significantly impacts cellular bioenergetics

  • Disruption leads to:

    • Reduced mitochondrial respiratory flux

    • Decreased ATP-linked respiration

    • Shift from Complex I to Complex II-dependent respiration

    • Global decrease in citric acid cycle metabolites

• Structural Insights:

  • Detailed structural analysis of NDUFB4's position within Complex I

  • Characterization of its interactions with both Complex I subunits and Complex III components

  • Understanding of how these interactions contribute to the higher-order organization of the respiratory chain

Implications and Future Directions:

• These findings highlight NDUFB4 as a critical "bridge" protein facilitating supercomplex formation

• The research provides strong evidence for the functional significance of respiratory supercomplexes in regulating cellular bioenergetics

• Understanding NDUFB4's role may provide insights into various diseases involving mitochondrial dysfunction, including neurodegeneration and metabolic syndromes

• Future research will likely focus on:

  • Additional interaction partners of NDUFB4

  • Regulatory mechanisms affecting these interactions

  • Potential therapeutic approaches targeting supercomplex stability

This recent work represents a significant advance in our understanding of how individual components like NDUFB4 contribute to the complex architecture and function of the mitochondrial respiratory chain.