Recombinant Candida glabrata Monopolar spindle protein 2 (MPS2)

Basic Research Questions

• What is Monopolar spindle protein 2 (MPS2) in Candida glabrata and what is its primary function?

MPS2 in C. glabrata is a 356-amino acid membrane protein (Q6FS52) that serves as a component of the spindle pole body (SPB) . Its primary function is facilitating the insertion of the nascent SPB into the nuclear envelope and ensuring proper SPB duplication. Research shows that MPS2 is an essential gene in fungi, and its deletion is typically lethal, preventing proper chromosome segregation during mitosis . The protein contains a transmembrane domain that anchors it in the nuclear membrane, positioning it to connect the SPB with the nuclear envelope .

Methodologically, researchers have characterized MPS2's essentiality through gene deletion experiments and conditional mutant studies that demonstrate cell cycle arrest with large buds and undivided nuclei when MPS2 function is compromised .

• How is the structure and localization of MPS2 characterized in experimental settings?

MPS2 can be characterized through several complementary approaches:

• Protein tagging: Researchers typically use epitope tagging (such as HA or GFP) at the C-terminus to visualize MPS2 localization while preserving function. For example, in similar yeast systems, MPS2 has been successfully tagged and observed to localize at the SPB .

• Chromatin immunoprecipitation (ChIP): While not directly applicable to MPS2 as it's not a DNA-binding protein, similar immunoprecipitation techniques have been used to study SPB-associated proteins .

• Structural analysis: The transmembrane domain of MPS2 can be predicted using bioinformatic tools and confirmed through membrane association experiments .

• Microscopy: Fluorescence microscopy of tagged MPS2 reveals its specific localization at the nuclear envelope where SPBs are inserted.

Researchers should note that modifications to MPS2 may affect protein function - for instance, C-terminal tagging could impair its interaction with binding partners .

• What is known about MPS2 expression patterns during the cell cycle in C. glabrata?

While C. glabrata-specific MPS2 expression data is limited, research on related fungal systems suggests that MPS2 expression may be regulated during the cell cycle. In Saccharomyces cerevisiae, components of the SPB show cell cycle-dependent regulation, with some proteins accumulating before SPB duplication .

To study MPS2 expression patterns, researchers can employ:

• Time-lapse microscopy with fluorescently tagged MPS2 to monitor protein levels throughout the cell cycle

• Synchronization experiments using methods like alpha-factor arrest (in compatible strains) followed by qRT-PCR or Western blotting to quantify MPS2 levels at different cell cycle stages

• Promoter analysis to identify potential cell cycle-specific regulatory elements

The expression and localization pattern of MPS2 is likely critical during G1/S transition when SPB duplication occurs, though further research specific to C. glabrata is needed to confirm this hypothesis.

Advanced Research Questions

• How does MPS2 interact with other proteins in the spindle pole body complex, and what methods can be used to characterize these interactions?

MPS2 functions as part of a complex network of proteins at the SPB. Based on studies in related fungi, MPS2 interacts with the SUN domain protein MPS3 to connect the half-bridge of the SPB to the core SPB structure . This interaction occurs between the C-terminus of MPS2 and the SUN domain of MPS3, forming a critical tether between SPB substructures.

Methods to characterize these interactions include:

Research on related SPB proteins in S. cerevisiae has shown that mutations in the MPS3 SUN domain or MPS2 C-terminus result in SPB duplication and karyogamy defects, consistent with aberrant half-bridge structures observed cytologically . Similar analyses in C. glabrata would likely yield important insights into species-specific aspects of this interaction.

• What role might MPS2 play in C. glabrata pathogenesis and antifungal resistance?

While direct evidence linking MPS2 to pathogenesis in C. glabrata is limited, several lines of indirect evidence suggest potential connections:

• Genomic Integrity: Proper spindle function, facilitated by MPS2, ensures accurate chromosome segregation. Genomic instability in C. glabrata has been linked to the development of antifungal resistance. Over 55% of clinical isolates exhibit mutations in the mismatch repair gene MSH2, conferring a mutator phenotype that promotes resistance acquisition .

• Stress Response: Spindle checkpoint proteins in related fungal pathogens like Candida albicans have been implicated in oxidative stress tolerance and morphogenesis , which are important virulence factors. Similar functions in C. glabrata would directly impact pathogenicity.

• Adaptability: C. glabrata exhibits remarkable genomic plasticity, with clinical isolates showing extensive chromosomal rearrangements and distinct karyotypes . Proper SPB function is essential for managing these chromosomal changes without triggering cell death.

Future research directions could include:

• Creating conditional MPS2 mutants in C. glabrata and assessing their virulence in animal models

• Examining MPS2 expression during macrophage infection, similar to studies that have mapped genome-wide RNA polymerase II occupancy in C. glabrata during this process

• Investigating whether MPS2 function is affected by antifungal exposure or environmental stressors

• How can recombinant C. glabrata MPS2 be effectively expressed, purified, and used for structural studies?

Producing recombinant MPS2 presents challenges due to its membrane association but can be accomplished using these methodological approaches:

Expression systems:

• E. coli: Express the soluble domains of MPS2 separately from the transmembrane region

• Yeast expression systems: Use S. cerevisiae or Pichia pastoris for full-length protein expression with native post-translational modifications

• Insect cells: Baculovirus expression system for complex eukaryotic proteins

Purification strategies:

• Affinity chromatography using histidine or GST tags

• For membrane-associated regions, detergent solubilization (e.g., DDM, LMNG) or nanodisc incorporation

• Size exclusion chromatography for final purification and buffer exchange

Structural studies:

• X-ray crystallography of soluble domains

• Cryo-EM for larger complexes

• NMR for dynamic regions

Functional validation:

• In vitro binding assays with purified interaction partners

• SPB assembly assays using recombinant components

• Complementation studies in MPS2-deficient yeast strains

For researchers using commercially available recombinant MPS2, typical product information includes:

• Protein purity ≥90% by SDS-PAGE

• Storage in Tris-based buffer with 50% glycerol

• Storage temperature recommendations: -20°C for long-term storage, 4°C for working aliquots up to one week

• What experimental approaches can be used to study the role of MPS2 in SPB duplication and nuclear envelope insertion in C. glabrata?

Several complementary approaches can be employed:

Genetic approaches:

• Conditional mutants: Since MPS2 is essential, use regulatable promoters (e.g., MET3 promoter used in C. albicans MPS1 studies) to control expression

• Temperature-sensitive mutants: Generate mutations that permit growth at permissive temperatures but fail at restrictive temperatures

• CRISPR interference: For transient knockdown of MPS2 expression

Cell biological approaches:

• Live-cell imaging: Use fluorescently tagged SPB components (e.g., Mps3-GFP as used in O. polymorpha) to track SPB duplication and behavior

• Electron microscopy: Examine SPB ultrastructure to detect defects in nuclear envelope insertion similar to studies showing cytoplasmic side of SPB differs structurally between G1 and anaphase

• Fluorescence recovery after photobleaching (FRAP): Study dynamics of MPS2 incorporation into the SPB

Biochemical approaches:

• Crosslinking coupled with mass spectrometry: Identify interaction networks and structural arrangements

• In vitro reconstitution: Attempt to reconstruct minimal SPB insertion machinery with purified components

A particularly valuable approach combines time-lapse microscopy with conditional mutants, allowing direct visualization of SPB duplication defects. For example, in O. polymorpha, time-lapse microscopy revealed that Spc72-GFP (another SPB component) became detectable approximately 4 minutes prior to anaphase initiation . Similar studies with MPS2 could reveal its temporal dynamics during SPB duplication in C. glabrata.

• How do mutations or alterations in MPS2 affect chromosome segregation and genetic stability in C. glabrata?

Mutations in MPS2 likely contribute to chromosome segregation defects and genetic instability through several mechanisms:

• Failed SPB insertion: If MPS2 mutations prevent proper SPB insertion into the nuclear envelope, this would lead to monopolar spindles and chromosome segregation failures

• Abnormal ploidy: Similar to observations in C. albicans where mutations in spindle checkpoint genes like MPS1 resulted in abnormal ploidy levels , MPS2 defects could lead to aneuploidy

• Genomic plasticity: C. glabrata clinical isolates already demonstrate considerable genomic diversity, with extensive chromosomal rearrangements . MPS2 dysfunction could exacerbate this plasticity

To study these effects, researchers can employ:

• Flow cytometry to detect changes in ploidy levels

• Chromosome loss assays using marked chromosomes

• Comparative genomic hybridization to detect large-scale chromosomal changes

• Microscopic observation of chromosome segregation using histone-fluorescent protein fusions

A particularly relevant finding is that C. glabrata appears to have evolved mechanisms to tolerate genomic instability, with many clinical isolates harboring mutations in DNA repair genes like MSH2 . This increased tolerance for genomic instability may interact with MPS2-related spindle defects in ways different from model organisms, potentially contributing to the pathogen's adaptability.

• How does C. glabrata MPS2 compare structurally and functionally to homologs in other fungal species?

Comparative analysis of MPS2 across fungal species reveals both conservation and divergence:

Methodological approaches to compare MPS2 across species include:

• Sequence alignment and phylogenetic analysis

• Heterologous expression studies

• Domain swap experiments to identify functionally critical regions

• Structural modeling based on available data from well-studied homologs

• What potential exists for targeting MPS2 or related SPB proteins for antifungal drug development?

MPS2 represents a promising antifungal target for several reasons:

• Essentiality: MPS2 is essential for fungal viability , making it a critical target that cannot be dispensed with

• Uniqueness to fungi: The fungal SPB differs significantly from the mammalian centrosome , potentially offering selectivity

• Drug-resistant strains: With increasing fluconazole and echinocandin resistance in C. glabrata , novel targets are urgently needed

Experimental approaches to explore MPS2 as a drug target include:

• High-throughput screening: Using conditional MPS2 mutants to identify compounds that specifically target cells with reduced MPS2 function

• Fragment-based drug discovery: Targeting specific interaction surfaces, such as the MPS2-MPS3 interface

• In silico screening: Computational docking studies to identify potential small molecule binders

• Chemical genetics: Synthetic lethality screens to identify pathways that become essential when MPS2 function is compromised

An analogous success story comes from a study identifying a small molecule inhibitor of another spindle protein (CaKip1) in C. albicans that showed fungicidal effects by inducing a dominant negative complex between CaKip1p and cellular tubulin , demonstrating the potential of targeting spindle components.