Recombinant Neosartorya fischeri Altered inheritance of mitochondria protein 31, mitochondrial (aim31)

What is Neosartorya fischeri aim31 protein and its primary function?

Altered inheritance of mitochondria protein 31 (aim31) in Neosartorya fischeri is a mitochondrial protein involved in maintaining mitochondrial morphology and function. Similar to other fungal mitochondrial proteins, aim31 likely plays critical roles in respiratory metabolism, mitochondrial inheritance during cell division, and stress response mechanisms . The protein contains conserved domains found across ascomycetes that facilitate integration into the mitochondrial membrane architecture.

How does recombinant aim31 differ structurally from native aim31?

Recombinant Neosartorya fischeri aim31 protein typically includes affinity tags (such as His or SUMO tags) for purification purposes, which are not present in the native protein. These modifications may result in slight conformational differences, although proper folding verification using techniques such as circular dichroism (CD) spectroscopy, NMR, or ESI-MS is essential to ensure structural integrity comparable to native forms . Key characteristics comparison:

What expression systems are most effective for producing recombinant Neosartorya proteins?

Based on successful recombinant production of other Neosartorya proteins, several expression systems have proven effective. For example, Penicillium chrysogenum-based expression systems have yielded approximately 40-times higher production of Neosartorya fischeri antifungal protein 2 (NFAP2) compared to native producers . For aim31 and similar mitochondrial proteins, the following expression systems are commonly utilized:

• E. coli expression systems: Suitable for high-yield production when protein folding is not complex

• Yeast expression systems (P. pastoris, S. cerevisiae): Provide eukaryotic post-translational processing

• Filamentous fungi expression systems (e.g., P. chrysogenum): Especially effective for fungal proteins requiring specific folding environments

The choice depends significantly on the intended application, required yield, and post-translational modification requirements.

How can researchers verify the correct folding and structural integrity of recombinant aim31?

Verification of proper folding for recombinant aim31 requires a multi-technique approach similar to that used for other complex fungal proteins:

• Electrospray Ionization Mass Spectrometry (ESI-MS): Confirms the exact molecular mass and can detect improper disulfide bond formation

• Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC): Analyzes purity and conformational homogeneity

• Electronic Circular Dichroism (ECD) spectroscopy: Evaluates secondary structure elements

• Nuclear Magnetic Resonance (NMR) spectroscopy: Provides detailed structural information at the atomic level

For isotope-labeled structural studies, 13C-HSQC fingerprint spectra can confirm structural identity between synthetic and recombinant versions by comparing methyl and aliphatic CH regions, as demonstrated with NFAP2 . This approach is particularly valuable when aiming to produce sufficient quantities of protein for detailed structural studies.

What purification strategies yield the highest purity for recombinant Neosartorya mitochondrial proteins?

Purification of mitochondrial proteins like aim31 typically requires a multistep approach to achieve research-grade purity (>90%):

• Initial capture using affinity chromatography (commonly Ni-NTA for His-tagged proteins or glutathione-sepharose for GST-tagged constructs)

• Tag removal using specific proteases (TEV, thrombin, or SUMO protease)

• Secondary purification using ion-exchange chromatography to separate cleaved tag from target protein

• Polishing step using size-exclusion chromatography to achieve final purity

This strategy typically yields preparations with ≥90% purity as determined by SDS-PAGE, similar to recombinant ASPF3 protein from N. fumigata . For functional studies, additional steps may include:

• Endotoxin removal for cell-based assays

• Buffer exchange into physiologically relevant conditions

• Concentration to experiment-specific requirements

What are the optimal storage conditions for maintaining long-term stability of recombinant aim31?

Based on storage protocols for similar fungal recombinant proteins, the following conditions are recommended for aim31:

For maximum stability, recombinant aim31 should be aliquoted immediately after purification to prevent protein degradation from repeated freeze-thaw cycles . After reconstitution of lyophilized material, adding glycerol to a final concentration of 5-50% before storage at -20°C/-80°C is advised.

How can researchers effectively assess mitochondrial localization of recombinant aim31 in heterologous systems?

To confirm proper mitochondrial localization of recombinant aim31, researchers should employ multiple complementary approaches:

• Fluorescence microscopy using GFP/RFP-tagged aim31 constructs co-localized with mitochondrial markers (MitoTracker dyes)

• Subcellular fractionation followed by Western blot analysis using organelle-specific markers

• Immunogold electron microscopy for precise localization within mitochondrial subcompartments

• Protease protection assays to determine membrane topology

Quantitative assessment of localization efficiency can be performed using high-content imaging systems that measure co-localization coefficients between tagged aim31 and established mitochondrial markers.

What functional assays are most informative for characterizing aim31's role in mitochondrial inheritance?

To characterize aim31's role in mitochondrial inheritance, researchers should consider the following functional assays:

• Mitochondrial morphology assessment using fluorescence microscopy in aim31 knockout vs. complemented strains

• Time-lapse imaging during cell division to track mitochondrial partitioning

• Genetic interaction studies with other known mitochondrial inheritance factors

• Mitochondrial DNA (mtDNA) maintenance assays to assess nucleoid distribution

• Respiratory competence measurements using oxygen consumption rate (OCR)

These assays can reveal whether aim31 functions similarly to other mitochondrial proteins such as peroxiredoxins that play roles in stress response and cellular protection. For instance, peroxiredoxins like ASPF3 in N. fumigata catalyze the reduction of hydrogen peroxide and are required for virulence .

How does recombinant aim31 interact with other mitochondrial proteins in reconstituted systems?

Interaction analysis between recombinant aim31 and other mitochondrial proteins requires:

• In vitro binding assays:

  • Pull-down assays using tagged recombinant proteins

  • Surface plasmon resonance (SPR) for kinetic and affinity measurements

  • Isothermal titration calorimetry (ITC) for thermodynamic parameters

• Structural interaction studies:

  • Chemical cross-linking coupled with mass spectrometry (XL-MS)

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS)

  • NMR-based protein-protein interaction mapping

• Functional reconstitution:

  • Liposome-based assays incorporating purified components

  • Respiration measurements in reconstituted proteoliposomes

  • Membrane potential assays using fluorescent probes

These approaches can help determine whether aim31 functions in protein complexes similar to other mitochondrial proteins characterized in Neosartorya species.

How can isotope-labeled recombinant aim31 be efficiently produced for structural studies?

Production of isotope-labeled recombinant aim31 for NMR studies requires specialized approaches:

• Expression system selection: E. coli remains the most cost-effective system for isotope labeling

• Media composition: Replace nitrogen and carbon sources with 15N-labeled ammonium chloride and 13C-glucose

• Expression optimization: Use lower growth temperatures (16-18°C) to enhance proper folding

• Sequential labeling strategies for specific amino acid labeling

Based on protocols developed for 13C/15N-labeled NFAP2, growing cultures in minimal media where standard nitrogen and carbon sources are replaced with 0.3% (w/v) Na15NO3 and 1% (w/v) 13C-glucose has proven effective . This approach typically yields sufficient labeled protein for comprehensive NMR investigations to reveal tertiary structure and structural dynamics.

What structural domains of aim31 are critical for its function, and how can they be identified?

Identification of critical functional domains in aim31 can be approached through:

• Comparative sequence analysis: Alignment with homologous proteins across fungal species to identify conserved motifs

• Functional mapping using synthetic peptide fragments: Similar to approaches used for NFAP2 , where synthetic peptide fragments revealed that the mid-N-terminal part influences activity

• Site-directed mutagenesis: Targeted modification of conserved residues followed by functional assays

• Domain swapping experiments: Creating chimeric proteins with domains from related proteins

How does aim31 function compare between Neosartorya fischeri and related pathogenic species like Neosartorya fumigata?

Comparative analysis between N. fischeri aim31 and homologs in pathogenic species like N. fumigata (A. fumigatus) should address:

• Sequence conservation and divergence at amino acid level

• Expression patterns under various physiological conditions

• Subcellular localization differences

• Protein-protein interaction networks

• Phenotypic consequences of gene deletion/mutation

This comparative approach can reveal whether aim31 contributes to pathogenicity in N. fumigata, similar to how peroxiredoxin ASPF3 plays a role in virulence by protecting cells against oxidative stress and detoxifying peroxides . Understanding these differences can provide insights into the evolution of mitochondrial function in pathogenic versus non-pathogenic Neosartorya species.

How can researchers overcome solubility issues with recombinant aim31 expression?

Strategies to improve solubility of recombinant aim31 include:

• Optimization of expression conditions:

  • Lower induction temperature (16-18°C)

  • Reduced inducer concentration

  • Extended expression time (24-48 hours)

• Fusion tags that enhance solubility:

  • SUMO tag (has shown success with ASPF3 from N. fumigata)

  • MBP (maltose-binding protein)

  • Thioredoxin

  • GST (glutathione S-transferase)

• Buffer optimization during purification:

  • Inclusion of mild detergents (0.05-0.1% Triton X-100)

  • Higher salt concentrations (300-500 mM NaCl)

  • Addition of stabilizing agents (5-10% glycerol)

  • Use of arginine and glutamic acid (50-100 mM each)

These approaches have proven effective for other challenging mitochondrial membrane proteins and can be adapted for aim31.

What strategies can address protein degradation during recombinant aim31 purification?

To minimize degradation during purification:

• Work at 4°C throughout the purification process

• Include protease inhibitor cocktails in all buffers

• Add reducing agents (1-5 mM DTT or β-mercaptoethanol) if appropriate

• Minimize purification duration with optimized protocols

• Consider on-column cleavage of affinity tags to reduce handling steps

• Use gentle elution conditions to maintain protein integrity

For mitochondrial proteins specifically, inclusion of phospholipids or cardiolipin in later purification stages may help maintain native-like environments and stability.

How can researchers validate that recombinant aim31 retains native functional properties?

Functional validation requires multiple complementary approaches:

• Structural integrity assessment:

  • Circular dichroism to confirm secondary structure elements

  • Thermal stability assays (DSF/DSC) to compare melting temperatures

  • Limited proteolysis patterns comparison between native and recombinant proteins

• Complementation studies:

  • Rescue of aim31 knockout phenotypes in relevant fungal species

  • Restoration of mitochondrial morphology and inheritance patterns

• In vitro functional assays:

  • Membrane binding capacity using liposome flotation assays

  • Protein-protein interaction profiles with known binding partners

  • Activity assays specific to predicted protein function

Similar validation approaches have been successfully used for other Neosartorya proteins, confirming that recombinant versions can maintain functional equivalence to native proteins when properly expressed and folded .

How might CRISPR-Cas9 genome editing advance aim31 functional studies in Neosartorya species?

CRISPR-Cas9 technology offers several advantages for aim31 research:

• Precise genetic modifications:

  • Targeted knockout/knockdown for loss-of-function studies

  • Introduction of point mutations to study structure-function relationships

  • Endogenous tagging for visualization and purification of native complexes

• Multiplexed gene editing:

  • Simultaneous modification of aim31 and interacting partners

  • Creation of strain libraries with varying levels of aim31 expression

• Regulatory studies:

  • Modification of aim31 promoter regions to study expression control

  • CRISPRi approaches for conditional repression in essential contexts

These approaches can provide insights into aim31 function that complement recombinant protein studies by examining the protein in its native cellular context.

What high-throughput approaches could identify novel interaction partners of aim31?

Modern high-throughput methods for discovering aim31 interaction partners include:

• Proximity-labeling approaches:

  • BioID or TurboID fusion to aim31 for in vivo labeling of proximal proteins

  • APEX2 labeling for mitochondria-specific interactome mapping

• Mass spectrometry-based methods:

  • Quantitative immunoprecipitation combined with knockout (QUICK)

  • Stable isotope labeling with amino acids in cell culture (SILAC)

  • Label-free quantitative proteomics of affinity-purified complexes

• Library screening approaches:

  • Yeast two-hybrid screening against normalized fungal cDNA libraries

  • Protein fragment complementation assays (PCA)

These methods can reveal both stable and transient interactions, providing a comprehensive view of aim31's role within mitochondrial protein networks.

How might structural biology advances further our understanding of aim31 function?

Emerging structural biology techniques offer new possibilities for aim31 research:

• Cryo-electron microscopy:

  • Single-particle analysis of aim31 complexes

  • Tomography of aim31 in mitochondrial membrane contexts

• Integrative structural biology:

  • Combining NMR, X-ray crystallography, and computational modeling

  • Molecular dynamics simulations to understand conformational dynamics

• In-cell structural studies:

  • In-cell NMR to study aim31 structure in native environment

  • High-resolution fluorescence approaches like FRET and super-resolution microscopy

The application of these techniques could reveal how aim31's structure relates to its function in mitochondrial inheritance and morphology maintenance, similar to the structural insights gained for other fungal proteins through NMR and other spectroscopic methods .