Recombinant Candida glabrata Altered inheritance of mitochondria protein 31, mitochondrial (AIM31)

What is AIM31 protein in Candida glabrata and what are its alternative names?

AIM31 (Altered inheritance of mitochondria protein 31) is also known as RCF1 (Respiratory supercomplex factor 1, mitochondrial) in Candida glabrata. It is a mitochondrial protein consisting of 158 amino acids that plays a role in respiratory function and mitochondrial inheritance. The protein is identified by UniProt ID Q6FSW5 and gene locus CAGL0G07315g . This protein belongs to the family of mitochondrial factors involved in the assembly and stability of respiratory complexes, which are crucial for energy metabolism in this opportunistic fungal pathogen.

What are the optimal conditions for expressing recombinant AIM31 in E. coli?

For optimal expression of recombinant AIM31 in E. coli, the following methodological approach is recommended:

• Vector selection: Use a pET-based expression vector with an N-terminal His-tag to facilitate purification.

• E. coli strain: BL21(DE3) or Rosetta(DE3) strains are recommended, as they are designed for high-level protein expression.

• Culture conditions:

  • Grow culture at 37°C until OD600 reaches 0.6-0.8

  • Induce with 0.5-1.0 mM IPTG

  • Reduce temperature to 18-25°C post-induction

  • Continue expression for 16-18 hours

This approach minimizes inclusion body formation and produces soluble protein, which is particularly important for mitochondrial proteins like AIM31 that may have transmembrane domains or complex folding requirements .

How should researchers store and reconstitute recombinant AIM31 protein to maintain optimal activity?

Based on product specifications, recombinant AIM31 requires careful handling:

• Storage recommendations:

  • Store lyophilized powder at -20°C/-80°C upon receipt

  • After reconstitution, prepare working aliquots to avoid repeated freeze-thaw cycles

  • Working aliquots can be stored at 4°C for up to one week

• Reconstitution protocol:

  • Briefly centrifuge the vial before opening

  • Reconstitute in deionized sterile water to 0.1-1.0 mg/mL

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

  • Default recommended final glycerol concentration is 50%

• Stability considerations:

  • Avoid repeated freeze-thaw cycles as this significantly reduces protein activity

  • For experiments requiring extended use, maintain aliquots at 4°C rather than repeatedly freezing and thawing

How does AIM31/RCF1 contribute to mitochondrial function in Candida glabrata?

AIM31/RCF1 plays a critical role in maintaining mitochondrial respiratory function in Candida glabrata through several mechanisms:

• Respiratory chain assembly: It functions as a respiratory supercomplex factor, facilitating the assembly and stability of respiratory chain complexes in the mitochondrial inner membrane.

• Mitochondrial inheritance: As the name suggests (Altered inheritance of mitochondria), it participates in ensuring proper inheritance of mitochondria during cell division, which is essential for fungal viability and growth.

• Oxidative stress response: Similar to other mitochondrial proteins in C. glabrata, AIM31 likely contributes to the cell's ability to respond to oxidative stress, which is critically important during infection when the pathogen encounters reactive oxygen species produced by host immune cells .

Experimental evidence from studies with other Candida species suggests that disruption of mitochondrial proteins often results in growth defects under stress conditions, reduced virulence, and altered morphogenesis, highlighting the importance of these proteins in pathogenicity.

What experimental approaches can be used to assess AIM31's role in C. glabrata virulence?

To investigate AIM31's role in C. glabrata virulence, researchers should consider the following methodological approaches:

• Gene deletion studies:

  • Generate AIM31/RCF1 knockout strains using CRISPR-Cas9 or traditional homologous recombination

  • Create reconstituted strains by reintroducing the wild-type gene for validation

  • Compare growth characteristics in standard media and under stress conditions

• Phenotypic assays:

  • Assess growth under various stress conditions (oxidative, nutrient limitation, pH stress)

  • Evaluate biofilm formation capacity

  • Test susceptibility to antifungal drugs

• In vivo infection models:

  • Mouse systemic infection model with tail vein injection (5×10^8 or 1×10^9 cells/ml)

  • Organ colonization assessment after 7 days post-infection

  • Comparison of CFU counts in target organs between wild-type and mutant strains

• Ex vivo interaction studies:

  • Macrophage survival assays

  • Neutrophil killing assays

  • Host cell adhesion assays

Similar studies with autophagy-related genes in C. glabrata have demonstrated that disruption of key cellular processes can affect virulence by impairing the pathogen's ability to adapt to host environments and resist immune defenses .

How does AIM31 compare functionally to similar proteins in Candida albicans and what are the implications for inter-species interactions?

Comparative analysis between C. glabrata AIM31 and its homologs in C. albicans reveals important functional differences with implications for research on inter-species interactions:

• Evolutionary divergence:

  • C. glabrata is phylogenetically closer to Saccharomyces cerevisiae than to C. albicans

  • This evolutionary distance is reflected in different mitochondrial protein functions

• Functional comparison:

  • Unlike C. albicans, which regularly undergoes morphological transitions, C. glabrata remains in yeast form

  • Mitochondrial proteins like AIM31 may serve specialized functions in C. glabrata's adaptation to host environments without morphological switching

• Inter-species interactions:

  • Recent research has revealed that C. glabrata and C. albicans engage in molecular communication during co-infection

  • C. glabrata secretes proteins (like Yhi1) that induce hyphal growth in C. albicans, which is essential for host tissue invasion

  • This raises the question of whether mitochondrial proteins like AIM31 might indirectly influence these inter-species interactions through metabolic regulation

Understanding these comparative aspects is crucial for researchers investigating polymicrobial infections, as the presence of C. albicans has been shown to be nearly essential for host colonization by C. glabrata in mixed-species invasive candidiasis .

What are the structural domains of AIM31 that could be targeted for antifungal development?

Analysis of AIM31's structure reveals potential domains that could serve as targets for novel antifungal development:

• Key structural features:

  • The IVYHCK motif at positions 33-38 appears to be important for protein function

  • The N-terminal region (first 30 amino acids) contains a potential mitochondrial targeting sequence

  • The central hydrophobic region likely forms a transmembrane domain essential for proper localization

• Targetable domains:

  • The IVYHCK region represents a potentially fungal-specific motif that could be targeted

  • Interfaces where AIM31 interacts with other respiratory complex proteins

  • Regions essential for protein-protein interactions within the mitochondrial membrane

• Therapeutic approach considerations:

  • Peptide-based inhibitors designed to mimic critical interaction domains

  • Small molecule compounds that disrupt protein-protein interactions

  • Compounds that prevent proper folding or localization of the protein

Recent research on other Candida proteins has demonstrated the potential of targeting unique peptide motifs as a strategy for developing novel antifungals. For example, the discovery of a synthetic peptide derivative (Yhi12-13) that demonstrates antifungal activity against both C. albicans and C. glabrata highlights the promise of this approach .

What are the common challenges in producing soluble recombinant AIM31 and how can they be addressed?

Researchers frequently encounter several challenges when expressing mitochondrial membrane proteins like AIM31:

• Inclusion body formation:

  • Challenge: AIM31 has hydrophobic regions that may cause aggregation during expression

  • Solution: Lower induction temperature (16-18°C), reduce IPTG concentration (0.1-0.2 mM), and use specialized E. coli strains like C41(DE3) designed for membrane protein expression

• Protein misfolding:

  • Challenge: Improper folding due to absence of mitochondrial chaperones in E. coli

  • Solution: Co-express with molecular chaperones (GroEL/GroES), use fusion partners like thioredoxin or NusA to enhance solubility

• Low yield:

  • Challenge: Mitochondrial proteins often express at lower levels

  • Solution: Optimize codon usage for E. coli, use high-cell-density fermentation, and consider auto-induction media

• Purification difficulties:

  • Challenge: Maintaining protein stability during purification

  • Solution: Include stabilizing agents (glycerol, specific detergents), perform purification at 4°C, and use buffer systems optimized for membrane proteins

Researchers should consider pilot experiments to determine the optimal expression and purification conditions for their specific application, as the requirements may vary depending on the downstream applications .

How can researchers verify the functional activity of recombinant AIM31 after purification?

To verify that purified recombinant AIM31 maintains its functional activity, researchers should perform multiple complementary assays:

• Structural integrity assessment:

  • Circular dichroism (CD) spectroscopy to confirm proper secondary structure

  • Size-exclusion chromatography to verify the protein exists in the expected oligomeric state

  • Thermal shift assays to assess protein stability

• Functional assays:

  • In vitro reconstitution with mitochondrial membrane components

  • Assessment of interaction with known binding partners using pull-down assays

  • Measurement of AIM31's ability to facilitate respiratory complex assembly

• Complementation studies:

  • Transform AIM31-deficient C. glabrata strains with the recombinant protein

  • Assess restoration of phenotypes such as growth under respiratory conditions

  • Measure mitochondrial function parameters (membrane potential, oxygen consumption)

• Activity verification table:

These complementary approaches provide a comprehensive assessment of both structural integrity and functional activity of the recombinant protein .

How does AIM31 function relate to C. glabrata autophagy and virulence mechanisms?

The relationship between AIM31 and autophagy in C. glabrata provides important insights into virulence mechanisms:

• Mitochondrial-autophagy crosstalk:

  • Mitochondrial proteins like AIM31 may influence mitochondrial dynamics, which can trigger autophagy responses

  • Disruption of mitochondrial function often leads to increased autophagy as a compensatory mechanism

• Autophagy's role in virulence:

  • Autophagy contributes to C. glabrata virulence by conferring resistance to unstable nutrient environments and immune defense mechanisms

  • Autophagy-deficient strains (e.g., Cgatg1Δ) show growth defects under nitrogen starvation and in the presence of H₂O₂

• Potential interconnection:

  • AIM31's function in maintaining mitochondrial homeostasis likely influences the cell's ability to adapt to stress

  • Studies in other fungi have shown that mitochondrial dysfunction can trigger compensatory autophagy responses

• Research implications:

  • Investigating the relationship between AIM31 and autophagy may reveal new aspects of C. glabrata pathogenicity

  • Dual targeting of mitochondrial function and autophagy could represent a promising therapeutic strategy

Understanding this interconnection is particularly relevant as C. glabrata has become an emerging threat in healthcare settings, with increasing incidences of invasive Candida infections that are challenging to diagnose, especially in multimodal invasive candidiasis without a positive blood culture .

What role might AIM31 play in C. glabrata's resistance to antifungal treatments?

AIM31's potential contribution to antifungal resistance in C. glabrata can be examined through several mechanistic pathways:

• Metabolic adaptation:

  • Proper mitochondrial function, which AIM31 supports, may allow C. glabrata to adapt its metabolism when exposed to antifungals

  • Metabolic flexibility is a known factor in C. glabrata's intrinsic resistance to azole antifungals

• Stress response pathways:

  • Mitochondrial proteins influence cellular responses to oxidative stress, which is often induced by antifungal treatment

  • The interaction between mitochondrial function and other stress response pathways may contribute to survival during drug exposure

• Energy production for efflux systems:

  • Efficient mitochondrial function provides the energy required for drug efflux pumps

  • These pumps actively export antifungal compounds from the cell, reducing their effectiveness

• Research directions:

  • Investigate whether AIM31 disruption alters susceptibility to different classes of antifungals

  • Examine potential synergistic effects between AIM31 inhibition and conventional antifungal treatments

  • Analyze AIM31 expression levels in clinical isolates with different antifungal resistance profiles

This research is particularly important given C. glabrata's inherent resistance to first-line antifungal drugs, which necessitates tailored courses of antifungals for effective treatment .