Recombinant Candida glabrata Mitochondrial import inner membrane translocase subunit TIM50 (TIM50)

What is the structure and function of Candida glabrata TIM50?

Candida glabrata TIM50 is a subunit of the TIM23 complex (Translocase of the Inner Mitochondrial membrane) that plays a crucial role in protein import into mitochondria. The protein spans the inner membrane with a single transmembrane segment and exposes a large hydrophilic domain in the intermembrane space . The full-length mature C. glabrata TIM50 protein consists of amino acids 36-485, with an amino acid sequence that includes key functional domains .

The protein's primary function is to act as a receptor for presequence-containing proteins that are destined for the mitochondrial matrix or inner membrane, facilitating their transfer from the TOM (Translocase of the Outer Membrane) complex to the TIM23 complex . This transfer is essential for proper mitochondrial protein import and, consequently, mitochondrial function.

Structural elements of C. glabrata TIM50:

How essential is TIM50 for Candida glabrata viability?

TIM50 is an essential gene for C. glabrata viability, as demonstrated through gene disruption studies. When the TIM50 gene was disrupted in a diploid yeast strain by integration of the HIS3 gene of Candida glabrata, and the cells were induced to sporulate, tetrad analysis revealed that only spores carrying the non-disrupted TIM50 were viable . This indicates that TIM50 is indispensable for the vegetative growth of C. glabrata, likely due to its vital role in mitochondrial protein import.

Research methodology for establishing gene essentiality:

• Create a diploid strain heterozygous for TIM50

• Induce sporulation and perform tetrad analysis

• Verify the presence/absence of TIM50 in viable spores

• Confirm that only spores containing TIM50 are viable

What are optimal methods for expressing and purifying recombinant C. glabrata TIM50?

Expression system recommendations:

The most effective system for expressing recombinant C. glabrata TIM50 is E. coli, which has been successfully used to produce His-tagged versions of the full-length mature protein (amino acids 36-485) . For optimal expression:

• Vector selection: Use a bacterial expression vector containing:

  • Strong inducible promoter (T7 or similar)

  • N-terminal His-tag for purification

  • Appropriate selection marker

• Expression conditions:

  • Culture growth: 37°C until OD600 reaches 0.6-0.8

  • Induction: Lower temperature (16-25°C) with IPTG (0.2-0.5 mM)

  • Extended expression period (16-20 hours) to maximize protein folding

• Purification protocol:

  • Lyse cells using appropriate buffer (Tris/PBS-based, pH 8.0)

  • Purify using Ni-NTA affinity chromatography

  • Perform size exclusion chromatography to enhance purity

  • Add 6% trehalose as a stabilizing agent

  • Consider final formulation with 5-50% glycerol for long-term storage at -20°C/-80°C

• Storage recommendations:

  • Store as lyophilized powder or in solution with glycerol

  • Avoid repeated freeze-thaw cycles

  • Maintain working aliquots at 4°C for up to one week

What experimental approaches can effectively evaluate TIM50 function in C. glabrata?

Several complementary approaches can be used to study TIM50 function in C. glabrata:

• Conditional expression systems:

  • Replace the native TIM50 promoter with an inducible promoter (e.g., GAL promoter)

  • Shift cells from permissive to non-permissive conditions

  • Monitor growth defects and mitochondrial protein import efficiency

• Domain deletion and mutagenesis:

  • Generate constructs lacking specific domains (e.g., presequence binding domain)

  • Create point mutations in conserved residues

  • Transform mutant constructs into a TIM50 deletion strain carrying wild-type TIM50 on a URA plasmid

  • Chase out the wild-type copy on 5-fluoroorotic acid medium

• Functional assays:

  • In vitro import assays with isolated mitochondria

  • Protein crosslinking to identify interaction partners

  • Blue native PAGE to assess complex integrity

  • Mitochondrial membrane potential measurements

• Virulence assessment:

  • Galleria mellonella infection model for preliminary virulence screening

  • Neutropenic mouse model for definitive virulence studies

How might TIM50 contribute to C. glabrata virulence mechanisms?

While direct evidence linking TIM50 to C. glabrata virulence is limited in the provided search results, several potential mechanisms can be proposed based on its essential function in mitochondrial protein import:

• Energy metabolism support:

  • TIM50 ensures proper mitochondrial function, which is critical for energy production

  • Adequate energy levels are required for C. glabrata to proliferate within host environments

  • Studies with other C. glabrata proteins have shown that the ability to proliferate in Galleria mellonella hemolymph correlates with virulence

• Stress resistance connection:

  • Proper mitochondrial function is essential for resistance to various stressors encountered during infection

  • Similar to other essential mitochondrial components, TIM50 may indirectly contribute to stress resistance

  • For example, CgDtr1, another C. glabrata protein, confers resistance to oxidative and acetic acid stress within phagocytes

• Potential interaction with known virulence factors:

  • C. glabrata virulence involves multiple factors including adhesins and stress response proteins

  • TIM50 may influence the expression or function of these factors through its role in mitochondrial protein import

  • Microevolution within patients affects cell surface proteins and genes involved in drug resistance

Research approach for investigating TIM50's role in virulence:

• Create conditional TIM50 mutants with reduced expression

• Evaluate their ability to survive within macrophages

• Assess their resistance to oxidative stress and other phagocyte killing mechanisms

• Study their proliferation in infection models like G. mellonella

How does mitochondrial function influence C. glabrata pathogenesis compared to other Candida species?

Comparing mitochondrial function between Candida species provides valuable insights into their differing pathogenesis mechanisms:

• C. glabrata vs. C. albicans mitochondrial differences:

  • C. glabrata mitochondrial genome is particularly diverse, with reduced conserved sequence and protein-encoding genes in non-reference ST15 isolates

  • This diversity may contribute to C. glabrata's unique niche adaptation and pathogenicity

  • Both species have Tim50 homologs, but sequence comparison reveals distinct features

• Distinct metabolic adaptations:

  • C. glabrata is more closely related to Saccharomyces cerevisiae than to C. albicans

  • C. glabrata has evolved to adapt to glucose-limited environments and can survive within nutrient-poor niches

  • Mitochondrial function may be differentially regulated between species to support their distinct metabolic requirements

• Interspecies interactions:

  • Recent research has revealed that C. glabrata secretes a unique small protein (Yhi1) that induces hyphal growth in C. albicans, which is essential for host tissue invasion

  • This interaction is regulated through the mating MAPK signaling pathway despite C. glabrata's preferred asexual reproduction

  • Such interactions may indirectly involve mitochondrial functions

Comparative analysis of TIM50 amino acid sequences:

How can mutations in TIM50 be used to study mitochondrial protein import in C. glabrata?

Targeted mutations in TIM50 provide a powerful approach to dissect the mechanisms of mitochondrial protein import in C. glabrata:

• Random mutagenesis approach:

  • Generate a library of random Tim50 mutants

  • Screen for temperature-sensitive phenotypes

  • Identify residues essential for Tim50 function

  • Map mutations to specific functional domains

• Domain-specific mutations:

  • Target the presequence binding domain (PBD)

  • Create Tim50ΔPBD constructs to assess the role of presequence recognition

  • Evaluate effects on matrix protein import versus inner membrane protein insertion

  • Determine if outer membrane translocation is affected

• Interaction surface mapping:

  • Mutations in specific surface patches can impair Tim50-Tim23 interactions

  • Two distinct regions of Tim50 have been identified that play roles in interaction with Tim23

  • Similar approaches can map interaction surfaces with precursor proteins

• Experimental workflow for studying Tim50 mutations:

  • Generate mutant constructs using site-directed mutagenesis

  • Transform into a strain with Tim50 under control of a regulatable promoter

  • Deplete endogenous Tim50 by promoter repression

  • Analyze phenotypes:

    • Growth at different temperatures

    • Mitochondrial morphology and function

    • Protein import efficiency for different types of precursors

What methodologies are available for studying protein-protein interactions involving TIM50?

Several complementary approaches can be employed to study TIM50 interactions:

• In vivo crosslinking:

  • Site-specific photocrosslinking using benzoyl phenylalanine (BPA) incorporation

  • Analyze crosslinked products by immunoprecipitation and mass spectrometry

  • Map interaction sites between Tim50 and precursor proteins or other translocase components

• Co-immunoprecipitation studies:

  • Tag Tim50 with HA or other epitope tags

  • Solubilize mitochondrial membranes under mild conditions

  • Immunoprecipitate Tim50 and identify interacting partners

  • Verify interactions under different conditions (e.g., active import vs. resting state)

• Reconstitution approaches:

  • Express and purify Tim50 and potential interaction partners

  • Perform in vitro binding assays

  • Use techniques like surface plasmon resonance to quantify binding kinetics

  • Reconstitute minimal interaction systems in liposomes

• Genetic interaction screens:

  • Synthetic genetic array analysis with Tim50 conditional mutants

  • Identify genes that show synthetic lethal or synthetic sick interactions

  • Map the network of functional interactions in mitochondrial protein import

• Bimolecular fluorescence complementation:

  • Split fluorescent proteins (e.g., GFP) are fused to potential interacting partners

  • Interaction brings the fragments together, restoring fluorescence

  • Can be used to visualize interactions in living cells

How does C. glabrata TIM50 differ from other fungal species, and what are the implications for drug development?

Comparative analysis of TIM50 across fungal species reveals important differences that could be exploited for selective drug targeting:

• Sequence divergence:

  • C. glabrata TIM50 shares ~80% similarity with S. cerevisiae but only ~60-70% with C. albicans

  • The human homolog (TIMM50) shares only about 29% amino acid identity with fungal TIM50

  • These differences suggest potential for selective targeting of fungal TIM50

• Functional conservation and divergence:

  • Core functions in mitochondrial protein import are conserved

  • Species-specific adaptations may exist, particularly in regulatory domains

  • Differential importance in virulence mechanisms between species

• Structural implications:

  • Presequence binding domain (PBD) is critical for function

  • Species-specific differences in this domain could affect substrate specificity

  • Targeting unique structural features could provide species selectivity

• Drug development strategies:

  • Target the presequence binding domain of TIM50

  • Focus on regions with low homology to human TIMM50

  • Design peptidomimetic inhibitors that compete with presequences

  • Develop compounds that disrupt Tim50-Tim23 interactions

• Methodological approach for comparative studies:

  • Perform detailed sequence alignments and structural modeling

  • Express recombinant TIM50 from different species

  • Compare biochemical properties and interaction partners

  • Test cross-species complementation to identify functionally divergent regions

What is known about the evolution of TIM50 in Candida species and its relationship to pathogenicity?

The evolution of TIM50 in Candida species provides insights into mitochondrial adaptation and potential links to pathogenicity:

• Evolutionary conservation:

  • TIM50 is highly conserved among fungi due to its essential role in mitochondrial function

  • Sequence analysis shows it belongs to a core set of proteins preserved across fungal evolution

  • Despite conservation, species-specific variations exist, particularly in non-catalytic regions

• Mitochondrial genome diversity in C. glabrata:

  • C. glabrata exhibits remarkable mitochondrial genome diversity compared to other Candida species

  • Population genetic studies have revealed hypervariable mitochondrial genomes

  • This diversity may influence the function of the mitochondrial import machinery, including TIM50

• Microevolution during infection:

  • In-patient microevolution has been observed in recurrent cases of candidiasis

  • Changes affect cell surface proteins and genes involved in drug resistance

  • Similar adaptive processes may affect mitochondrial function during persistent infection

• Methodological approaches for evolutionary studies:

  • Comparative genomics across Candida species

  • Population genetic analysis of clinical isolates

  • Assessment of selective pressures on TIM50 and related genes

  • Functional complementation experiments between species

Comparison of TIM50 across Candida species:

What are the major technical challenges in studying C. glabrata TIM50, and how can researchers overcome them?

Researchers face several technical challenges when studying C. glabrata TIM50:

• Gene essentiality complications:

  • TIM50 is essential, making knockout studies impossible

  • Solution: Use conditional expression systems (e.g., GAL or MET25 promoters)

  • Method: Replace the native promoter with a regulatable one to control expression levels

• Membrane protein purification difficulties:

  • Tim50 is an integral membrane protein, making it challenging to purify in native form

  • Solution: Express the soluble domain (presequence binding domain) separately

  • Alternative: Use mild detergents optimized for mitochondrial membrane proteins

• Limited genetic tools in C. glabrata:

  • Fewer genetic manipulation tools compared to S. cerevisiae

  • Solution: Adapt CRISPR-Cas9 systems from other yeast species

  • Method: Optimize transformation protocols specifically for C. glabrata

• Functional assays challenges:

  • Mitochondrial import assays require specialized equipment

  • Solution: Develop simplified assays using fluorescent reporter proteins

  • Method: Create fusion proteins with split fluorescent reporters that indicate successful import

• Heterologous expression issues:

  • Expression of full-length TIM50 can be problematic

  • Solution: Optimize codon usage for the expression system

  • Method: Use fusion partners to enhance solubility and expression

How can researchers effectively study TIM50's role in virulence without compromising mitochondrial function?

• Domain-specific mutations:

  • Target non-essential domains or specific residues

  • Create partial loss-of-function mutants that maintain basic mitochondrial function

  • Screen for mutations that specifically affect stress response without compromising growth

• Controlled depletion studies:

  • Use auxin-inducible degron systems for rapid protein depletion

  • Time-course studies to separate immediate from secondary effects

  • Monitor both mitochondrial function and virulence traits during progressive depletion

• Interaction partner modulation:

  • Target TIM50 interaction partners rather than TIM50 itself

  • Identify and modulate specific interactions relevant to virulence

  • Use peptide inhibitors to disrupt specific interactions

• Model system adaptation:

  • Use the Galleria mellonella infection model for rapid screening

  • Develop cell culture-based assays to model host-pathogen interactions

  • Implement ex vivo infection models with human tissue samples

• Experimental design recommendations:

  • Include appropriate controls (wild-type and complemented strains)

  • Perform time-course studies to distinguish primary from secondary effects

  • Combine multiple approaches (genetics, biochemistry, cell biology) for comprehensive understanding

  • Use systems biology approaches to model the effects of TIM50 perturbation on cellular networks