Recombinant Lachancea thermotolerans Altered inheritance of mitochondria protein 31, mitochondrial (AIM31)

What is Lachancea thermotolerans and why is it important for mitochondrial research?

Lachancea thermotolerans (formerly known as Kluyveromyces thermotolerans) is a yeast species that has gained significant research interest due to its unique physiological and genetic characteristics. This yeast diverged after the appearance of anaerobic capability, approximately 125-150 million years ago, before the whole-genome duplication event that occurred around 100 million years ago . Notably, L. thermotolerans represents the first lineage after the loss of respiratory chain complex I, a crucial event that happened after the split of the Saccharomyces-Lachancea and Kluyveromyces-Eremothecium lineages .

The species is particularly valuable for mitochondrial research because it provides insights into the evolutionary development of the Crabtree effect and anaerobic growth capabilities in yeasts. Studying this species can help researchers understand the earliest molecular events that initiated the Crabtree effect in ancestral yeast species . Additionally, population genomic analysis has revealed highly conserved mitochondrial genomes in L. thermotolerans, making it an excellent model organism for studying mitochondrial inheritance and function .

What is the AIM31 protein and what is its known function?

The Altered inheritance of mitochondria protein 31 (AIM31) is a mitochondrial protein found in Lachancea thermotolerans. Based on its classification, AIM31 is involved in mitochondrial inheritance patterns . The protein consists of 160 amino acids with the sequence beginning with MSHLPSSFDGAEQDVDEMTF and ending with LQAKTSSSK .

While the specific molecular function of AIM31 in L. thermotolerans hasn't been extensively characterized in the available literature, its classification suggests it plays a role in ensuring proper distribution of mitochondria during cell division. The protein is likely involved in mitochondrial organization, potentially affecting the structural integrity of mitochondrial membranes or participating in protein complexes that regulate mitochondrial inheritance during yeast budding.

How does L. thermotolerans differ from Saccharomyces cerevisiae in terms of metabolic capabilities?

L. thermotolerans exhibits several distinctive metabolic features that differentiate it from the conventional winemaking yeast Saccharomyces cerevisiae:

• Lactic acid production: One of the most significant differences is L. thermotolerans' ability to synthesize substantial amounts of lactic acid during alcoholic fermentation. While S. cerevisiae produces no more than 0.4 g/L of lactic acid during must fermentation, L. thermotolerans can increase lactic acid concentration up to 16 g/L .

• Ethanol reduction: L. thermotolerans can metabolize a portion of hexoses into lactic acid rather than ethanol, resulting in lower ethanol content in the final product. This characteristic is particularly valuable for addressing challenges associated with climate change, such as higher sugar concentrations in grape musts .

• Acid balance: The increased titratable acidity from lactic acid production positively affects microbial stability and organoleptic characteristics of wines produced with L. thermotolerans .

• Adaptation signatures: Wine-related strains of L. thermotolerans show specific adaptations to the fermentative environment, including increased fitness in the presence of ethanol and sulfites, better assimilation of non-fermentable carbon sources like glycerol, and lower levels of residual fructose under fermentative conditions .

What experimental systems are appropriate for studying AIM31 function?

To effectively study AIM31 function, researchers should consider the following experimental approaches:

• Recombinant protein expression systems: For biochemical and structural studies, expressing recombinant AIM31 in systems like E. coli or other yeast species allows for protein purification and characterization. The protein can be stored in Tris-based buffer with 50% glycerol, as recommended for the commercially available recombinant protein .

• Gene deletion studies: Creating AIM31 knockout strains in L. thermotolerans to observe phenotypic changes related to mitochondrial inheritance and function. When designing these experiments, researchers should include appropriate controls to distinguish between direct effects of AIM31 deletion and secondary consequences.

• Fluorescent tagging: Using GFP or other fluorescent tags to visualize AIM31 localization within mitochondria and track mitochondrial distribution during cell division.

• Comparative genomics: Analyzing AIM31 sequence conservation across different L. thermotolerans strains and related yeast species can provide insights into its evolutionary importance and functional domains.

What methodologies are recommended for expressing and purifying recombinant L. thermotolerans AIM31?

When working with recombinant L. thermotolerans AIM31, researchers should consider the following methodological approaches:

• Expression system selection: E. coli BL21(DE3) or similar strains are commonly used for mitochondrial protein expression. For projects requiring native folding and post-translational modifications, yeast-based expression systems like Pichia pastoris may be preferable.

• Codon optimization: The coding sequence should be optimized for the expression host to improve protein yield. When expressing L. thermotolerans genes in E. coli, consider the significant GC content differences.

• Tag selection: A polyhistidine tag (6xHis) facilitates purification by immobilized metal affinity chromatography (IMAC). For studying protein-protein interactions, consider using a dual-tag system with both His and another tag like GST or MBP.

• Purification protocol:

  • Cell lysis: Sonication or French press for E. coli; glass bead disruption for yeast

  • Initial capture: IMAC with Ni-NTA resin

  • Further purification: Size exclusion chromatography to separate monomeric protein from aggregates

  • Buffer optimization: Tris-based buffer (pH 7.5-8.0) with 50% glycerol for storage, as used in commercial preparations

• Quality control: SDS-PAGE analysis, western blotting, and mass spectrometry to verify protein identity and purity. Circular dichroism spectroscopy to assess secondary structure integrity.

How can researchers investigate AIM31's role in mitochondrial inheritance during L. thermotolerans adaptation to fermentative environments?

Investigating AIM31's role in L. thermotolerans adaptation to fermentative environments requires an integrated approach:

• Strain collection and genotyping:

  • Collect L. thermotolerans strains from diverse environments, including wine-related and natural habitats

  • Use whole-genome sequencing to identify polymorphisms in AIM31 and related genes

  • Apply population genomic analysis to correlate AIM31 sequence variations with ecological niches

• Phenotypic characterization:

  • Assess mitochondrial morphology and distribution across strains using fluorescence microscopy

  • Evaluate respiratory capacity and fermentative efficiency

  • Measure fitness under various stress conditions relevant to winemaking (ethanol, sulfites, acidic pH)

• Experimental evolution:

  • Subject L. thermotolerans strains to serial transfers in wine-like medium

  • Monitor changes in AIM31 sequence and expression levels

  • Correlate changes with phenotypic adaptations

• Functional validation:

  • Create isogenic strains differing only in AIM31 alleles

  • Use CRISPR-Cas9 to introduce specific mutations identified in adapted strains

  • Perform complementation assays with different AIM31 variants

• Data analysis:

  • Apply statistical methods to identify correlations between AIM31 variants and phenotypic traits

  • Use machine learning approaches to predict the impact of specific mutations

  • Construct phylogenetic trees to trace the evolution of AIM31 in relation to adaptation events

This multifaceted approach would help elucidate whether changes in AIM31 contribute to the documented adaptation of L. thermotolerans to winemaking environments .

How does the genomic diversity of L. thermotolerans impact studies on mitochondrial inheritance proteins?

The genomic diversity of L. thermotolerans has significant implications for studying mitochondrial inheritance proteins like AIM31:

• Population structure considerations: L. thermotolerans exhibits a complex population structure with six well-defined groups primarily delineated by ecological origin . When designing experiments on mitochondrial inheritance, researchers must account for this structure to avoid confounding genetic background effects with protein-specific effects.

• Anthropization effects: Anthropized strains (particularly wine-related) show lower genetic diversity due to purifying selection imposed by the winemaking environment . This reduced diversity may impact the variability of mitochondrial inheritance proteins and potentially their function.

• Experimental design approach:

  • Include strains from multiple population groups in any comparative study

  • Control for genetic background effects by using isogenic strains differing only in the mitochondrial protein of interest

  • Consider the impact of domestication history when interpreting phenotypic differences

• Pangenome analysis: L. thermotolerans exhibits variation in gene content across strains, including genes involved in alternative carbon and nitrogen source assimilation . When studying mitochondrial inheritance, researchers should determine whether their strains of interest contain the complete set of interacting partners for proteins like AIM31.

• Mitochondrial genome conservation: Despite nuclear genome diversity, L. thermotolerans shows highly conserved mitochondrial genomes . This conservation may indicate strong selective pressure on mitochondrial functions, including inheritance mechanisms.

What analytical techniques are most informative for studying the structure-function relationship of AIM31?

To effectively investigate the structure-function relationship of AIM31, researchers should employ these analytical techniques:

These techniques should be applied in an integrated manner, with results from one approach informing the design of experiments using other methods.

How can researchers quantitatively assess the impact of AIM31 variants on mitochondrial function?

Quantitative assessment of AIM31 variants requires robust methodological approaches:

• Mitochondrial morphology quantification:

  • Fluorescence microscopy with mitochondria-specific dyes (e.g., MitoTracker)

  • Automated image analysis to measure parameters like mitochondrial number, size, and distribution

  • Time-lapse imaging to track inheritance patterns during cell division

• Respiratory function measurements:

  • Oxygen consumption rate using respirometry

  • Complex activity assays for individual respiratory chain components

  • Membrane potential assessment using potentiometric dyes

• Metabolic profiling:

  • Targeted metabolomics focusing on TCA cycle intermediates

  • Measurement of fermentation products, particularly lactic acid

  • Analysis of ethanol production efficiency

• Stress response quantification:

  • Growth curves under various stress conditions

  • Reactive oxygen species (ROS) measurement

  • Protein carbonylation assessment as indicator of oxidative damage

• Gene expression analysis:

  • RNA-Seq to identify genes differentially expressed in response to AIM31 variants

  • RT-qPCR for targeted analysis of mitochondrial genes

  • Proteomics to assess changes in mitochondrial protein composition

What are the optimal storage and handling conditions for recombinant AIM31 protein?

For optimal results when working with recombinant L. thermotolerans AIM31 protein, researchers should follow these storage and handling guidelines:

• Storage recommendations:

  • Store at -20°C for standard use

  • For extended storage, conserve at -20°C or -80°C

  • Maintain in Tris-based buffer with 50% glycerol, optimized for protein stability

  • Avoid repeated freezing and thawing cycles

  • Prepare working aliquots and store at 4°C for up to one week

• Thawing protocol:

  • Thaw aliquots on ice to prevent protein degradation

  • Centrifuge briefly after thawing to collect condensation

  • Avoid vortexing to prevent protein denaturation

• Quality control measures:

  • Verify protein integrity by SDS-PAGE before experimental use

  • Monitor activity using appropriate functional assays

  • Check for aggregation using dynamic light scattering when necessary

• Buffer considerations:

  • For functional studies, dilute from storage buffer into working buffer immediately before use

  • Consider additive screening to optimize buffer conditions for specific applications

  • Monitor pH stability, particularly for assays requiring specific pH conditions

How can researchers design experiments to distinguish between direct and indirect effects when studying AIM31 function?

Distinguishing between direct and indirect effects of AIM31 requires careful experimental design:

• Genetic approach strategies:

  • Create conditional knockout systems (e.g., tetracycline-regulated expression)

  • Use rapid depletion systems (e.g., auxin-inducible degron tags)

  • Employ temperature-sensitive alleles for acute functional disruption

  • Create point mutations affecting specific domains rather than whole-gene deletions

• Temporal analysis:

  • Monitor changes immediately following AIM31 depletion/inactivation

  • Establish a time course to differentiate primary from secondary effects

  • Use metabolic labeling to track newly synthesized proteins after AIM31 perturbation

• Spatial considerations:

  • Use high-resolution microscopy to correlate AIM31 localization with observed phenotypes

  • Employ mitochondrial subfractionation to determine precise submitochondrial localization

  • Assess effects on specific mitochondrial compartments (matrix, inner membrane, intermembrane space)

• Molecular interaction verification:

  • Confirm direct interactions using in vitro binding assays with purified components

  • Employ proximity labeling techniques (BioID, APEX) to identify nearest neighbors in vivo

  • Use FRET or BiFC to visualize interactions in living cells

• Controls and validation:

  • Include rescue experiments with wild-type protein to confirm specificity

  • Test multiple independent clones to rule out off-target effects

  • Compare results across different genetic backgrounds to establish robustness

What bioinformatic approaches are most useful for analyzing AIM31 in the context of L. thermotolerans population genomics?

When analyzing AIM31 in the context of L. thermotolerans population genomics, researchers should consider these bioinformatic approaches:

• Sequence analysis methods:

  • Multiple sequence alignment of AIM31 across L. thermotolerans strains

  • Calculation of nucleotide diversity (π) and Tajima's D to detect selection signatures

  • Identification of conserved domains and critical residues

  • Codon usage analysis to detect translation optimization

• Population structure analysis:

  • Principal Component Analysis (PCA) or STRUCTURE analysis to visualize population clustering

  • Phylogenetic tree construction to understand evolutionary relationships

  • FST calculation to quantify genetic differentiation between populations

  • Analysis of molecular variance (AMOVA) to partition genetic diversity

• Selection pressure assessment:

  • dN/dS ratio calculation to detect positive or purifying selection

  • McDonald-Kreitman test to compare polymorphism and divergence

  • Haplotype-based selection tests (e.g., iHS, XP-EHH)

  • Bayesian approaches to identify genomic regions under selection

• Comparative genomics framework:

  • Ortholog identification across yeast species

  • Synteny analysis to detect genomic rearrangements

  • Analysis of gene presence/absence variation in the pangenome

  • Identification of lineage-specific adaptations

• Correlation with phenotypic data:

  • Genome-wide association studies (GWAS) linking AIM31 variants to phenotypes

  • Integrative analysis combining genomic, transcriptomic, and phenotypic data

  • Machine learning approaches to predict functional impacts of variants

These approaches can help researchers understand how AIM31 variants contribute to the documented adaptation of L. thermotolerans to different environments, particularly the winemaking niche .

How should researchers interpret differences in AIM31 function between laboratory and natural isolates of L. thermotolerans?

Interpreting functional differences in AIM31 between laboratory and natural isolates requires careful consideration of several factors:

By systematically addressing these considerations, researchers can differentiate between strain-specific idiosyncrasies and true functional differences in AIM31 that contribute to adaptation.

How might AIM31 function relate to L. thermotolerans' unique lactic acid production capability?

The potential relationship between AIM31 function and L. thermotolerans' lactic acid production capability represents an intriguing research direction:

• Metabolic connection hypothesis:

  • Mitochondrial function influences carbon flux distribution in yeast cells

  • AIM31, as a mitochondrial protein, may impact respiratory efficiency and thus redirect carbon toward lactic acid production

  • Changes in mitochondrial inheritance patterns could affect the balance between respiratory and fermentative metabolism

• Evolutionary context:

  • Lactic acid production in wine-related strains is hypothesized to be an anthropization signature resulting from adaptation of Crabtree-positive yeasts to fermentative environments

  • AIM31 variants might contribute to this adaptation by modulating mitochondrial function under fermentative conditions

• Experimental approaches to explore this connection:

  • Compare AIM31 sequence and expression between high and low lactic acid-producing strains

  • Assess how AIM31 mutations affect lactic acid production in controlled fermentations

  • Measure mitochondrial function parameters in strains with varying lactic acid production capabilities

  • Investigate how AIM31 influences the expression of genes involved in lactic acid metabolism

• Metabolic engineering implications:

  • Understanding this relationship could enable the development of optimized strains for specific fermentation applications

  • Targeted modifications of AIM31 might allow fine-tuning of lactic acid production

This research direction could provide valuable insights into both the fundamental biology of L. thermotolerans and its applications in winemaking to address challenges related to climate change .

What emerging technologies might advance our understanding of AIM31 function in mitochondrial inheritance?

Several emerging technologies hold promise for advancing our understanding of AIM31 function:

• Advanced imaging techniques:

  • Super-resolution microscopy (PALM, STORM, STED) to visualize AIM31 localization with nanometer precision

  • Correlative light and electron microscopy (CLEM) to connect protein localization with ultrastructural context

  • Live-cell imaging with lattice light-sheet microscopy for dynamic studies of mitochondrial inheritance

• Single-cell technologies:

  • Single-cell RNA-Seq to detect cell-to-cell variability in AIM31 expression

  • Single-cell proteomics to quantify protein abundance at the individual cell level

  • Microfluidic approaches for tracking individual cells across generations

• Genome editing advances:

  • Base editing for precise introduction of point mutations without double-strand breaks

  • Prime editing for flexible DNA modifications with minimal off-target effects

  • CRISPR activation/interference systems for modulating AIM31 expression without genetic modification

• Structural biology developments:

  • AlphaFold2 and other AI-based structure prediction tools for modeling AIM31 structure

  • In-cell NMR to study protein structure in the native cellular environment

  • Integrative structural biology approaches combining multiple data sources

• Synthetic biology approaches:

  • Minimal synthetic mitochondria to test AIM31 function in simplified systems

  • Orthogonal translation systems for site-specific incorporation of unnatural amino acids

  • Engineered protein scaffolds to modulate AIM31 interactions

These technologies, applied individually or in combination, would provide unprecedented insights into AIM31's role in mitochondrial inheritance and potentially its contribution to L. thermotolerans' unique metabolic capabilities.