Recombinant Schizosaccharomyces pombe Putative mannan endo-1,6-alpha-mannosidase C1198.07c (SPBC1198.07c)

What is SPBC1198.07c and what is its biological significance in S. pombe?

SPBC1198.07c is a gene in the fission yeast Schizosaccharomyces pombe that encodes a putative mannan endo-1,6-alpha-mannosidase (EC 3.2.1.101). This enzyme catalyzes the random hydrolysis of (1→6)-α-D-mannosidic linkages in unbranched (1→6)-mannans . The protein has been classified as having anti-longevity effects, as deletion studies have shown that removing this gene increases chronological lifespan in S. pombe .

The biological significance of SPBC1198.07c lies in its potential role in glycoprotein processing and quality control in the endoplasmic reticulum (ER). While S. pombe was previously thought to lack ER α-mannosidase activity, more sensitive studies have detected an extremely feeble ER α-mannosidase activity in vivo that could not be detected in vitro . This suggests a possible role in the endoplasmic reticulum-associated degradation (ERAD) pathway, which targets misfolded glycoproteins for proteasomal degradation.

The enzyme belongs to a group of three proteins in S. pombe with potential α-mannosidase activity: Spmns1p, Spmns2p, and Spmnl1p. The SPBC1198.07c gene likely encodes Spmns1p, which shows higher similarity (56.8%) to S. cerevisiae ER α-mannosidase .

How is SPBC1198.07c related to aging processes in fission yeast?

Deletion of SPBC1198.07c in fission yeast has been demonstrated to increase chronological lifespan, as documented in genetic screening studies . This places SPBC1198.07c in the category of "anti-longevity" genes, meaning its normal function may actually promote aging processes in S. pombe.

The relationship between glycoprotein processing enzymes like SPBC1198.07c and aging is an emerging area of research. The mechanism by which SPBC1198.07c deletion extends lifespan may involve:

• Reduced ER stress through altered glycoprotein processing

• Modified cell wall integrity and stress responses

• Altered protein quality control mechanisms

• Changes in cellular signaling pathways that regulate aging

Researchers have used chronological lifespan assays in quiescent S. pombe cells deprived of nitrogen to study aging factors. These quiescent cells arrest in a differentiated G0-like state and can survive for more than 2 months, providing an excellent model for aging studies . Using barcode sequencing (Bar-seq) technology, scientists have profiled pooled deletion mutants, including SPBC1198.07c mutants, to assess their lifespans during long-term quiescence .

Understanding how SPBC1198.07c influences aging processes could provide valuable insights into fundamental mechanisms of cellular aging and potentially identify targets for interventions to extend lifespan.

What enzymatic activity does the SPBC1198.07c-encoded protein exhibit?

The SPBC1198.07c gene encodes a putative mannan endo-1,6-alpha-mannosidase (EC 3.2.1.101) with the systematic name 6-α-D-mannan mannanohydrolase . This enzyme catalyzes the following reaction:

Random hydrolysis of (1→6)-α-D-mannosidic linkages in unbranched (1→6)-mannans

The enzyme belongs to glycoside hydrolase family 76 (GH-76), which includes enzymes that cleave α-1,6-mannosidic linkages. Based on studies of similar enzymes, the reaction mechanism likely involves:

• Binding of the mannan substrate in the active site

• Nucleophilic attack on the anomeric carbon

• Formation of a glycosyl-enzyme intermediate

• Hydrolysis of the intermediate to release the cleaved mannan products

The activity can be detected through HPLC analysis of reaction products, with specific α-1,6-mannosidases (such as those from Xanthomonas manihotis) being used to verify the nature of the linkages formed .

Detection and quantification of SPBC1198.07c gene expression:

• RT-PCR and qRT-PCR:

  • Design primers specific to the SPBC1198.07c sequence

  • Extract RNA from S. pombe cells under various conditions

  • Perform reverse transcription followed by PCR amplification

  • For qRT-PCR, use appropriate reference genes for normalization

• Northern blotting:

  • Generate RNA probes specific to SPBC1198.07c

  • Hybridize with total RNA extracted from S. pombe

  • Quantify signal intensity to measure expression levels

• RNA-seq:

  • Perform high-throughput sequencing of the S. pombe transcriptome

  • Align reads to the reference genome

  • Quantify SPBC1198.07c expression relative to other genes

Detection and analysis of SPBC1198.07c protein:

• Western blotting:

  • Generate antibodies against SPBC1198.07c or use tag-specific antibodies

  • Extract proteins from S. pombe cells

  • Separate by SDS-PAGE and transfer to membrane

  • Detect with specific antibodies

• Immunofluorescence microscopy:

  • Use specific antibodies to localize SPBC1198.07c in fixed cells

  • Co-stain with markers for cell compartments (ER, Golgi, etc.)

Measurement of enzymatic activity:

• In vivo assays:

  • Label S. pombe cells with radioactive glucose

  • Extract and analyze protein-linked glycans by Endo H release

  • Identify Man8GlcNAc formation (indicative of α-mannosidase activity)

• In vitro enzymatic assays:

  • Use purified recombinant SPBC1198.07c protein

  • Incubate with appropriate substrates (synthetic or natural)

  • Detect products using HPLC, mass spectrometry, or colorimetric methods

  • Verify product identity using specific α-1,6-mannosidases

These methods provide researchers with a comprehensive toolkit for analyzing SPBC1198.07c expression, localization, and activity under various experimental conditions.

What experimental approaches can be used to study the enzymatic activity of recombinant SPBC1198.07c?

To characterize the enzymatic properties of recombinant SPBC1198.07c, researchers can employ a multifaceted experimental approach:

Enzyme Production and Purification:

• Expression systems:

  • E. coli: For His-tagged protein expression (demonstrated successful expression)

  • Baculovirus: For expression in insect cells with proper folding

  • Yeast: For expression in a similar eukaryotic environment

• Purification strategy:

  • Affinity chromatography using His-tag

  • Size exclusion chromatography for further purification

  • Verify purity by SDS-PAGE (target >85% purity)

Activity Assays:

• HPLC-based assays:
  Similar to those used for related mannosyltransferases :

  • Substrate preparation: α-Man-pNP (1.5 mM) as sugar acceptor

  • Donor: GDP-Man (5 mM)

  • Cofactor: Mn²⁺ (1.0 mM)

  • Reaction conditions: 30°C for 16 h

  • Analysis: Reverse-phase HPLC using a C18 column with UV detection

  • Product confirmation: Digestion with α-(1→6)-specific mannosidase from Xanthomonas manihotis

• Spectrophotometric assays:

  • Use synthetic substrates with chromogenic or fluorogenic leaving groups

  • Monitor release of p-nitrophenol or 4-methylumbelliferone

• Mass spectrometry:

  • Analyze reaction products to determine exact structures

  • Perform kinetic measurements using multiple reaction monitoring (MRM)

Kinetic Analysis:

• Determine kinetic parameters:

  • Vary substrate concentrations to determine Km and Vmax

  • Test pH and temperature optima

  • Evaluate metal ion requirements

• Inhibitor studies:

  • Test known mannosidase inhibitors (e.g., kifunensin)

  • Determine inhibition constants (Ki values)

  • Perform structure-activity relationship studies

Structure-Function Analysis:

• Site-directed mutagenesis:

  • Target predicted catalytic residues

  • Create mutations at substrate binding sites

  • Assess effects on activity and substrate specificity

• Domain analysis:

  • Create truncated proteins to identify minimal catalytic domain

  • Generate chimeric proteins with related enzymes

These approaches will provide comprehensive characterization of the enzymatic properties of SPBC1198.07c, yielding insights into its substrate specificity, catalytic mechanism, and potential roles in glycoprotein processing.

How does deletion of SPBC1198.07c affect chronological lifespan in S. pombe, and what are the potential molecular mechanisms?

The deletion of SPBC1198.07c has been shown to increase chronological lifespan (CLS) in S. pombe , classifying it as an anti-longevity gene. Understanding the mechanisms behind this lifespan extension requires sophisticated experimental approaches:

Experimental Methods to Study Lifespan Effects:

• Chronological Lifespan Assays:

  • Culture wild-type and ΔSPBC1198.07c strains to stationary phase

  • Monitor viability over time using colony-forming unit (CFU) counts

  • Use propidium iodide staining and flow cytometry to assess cell death

  • Implement parallelized methods such as Bar-seq for high-throughput analysis

• Competition-Based Approaches:

  • Grow mixed populations of wild-type and mutant cells

  • Track relative abundance over time using strain-specific markers

  • Analyze using deep sequencing of strain-specific barcodes

  Strain	Longevity Category	Genetic Manipulation	Lifespan Effect	Reference
  ΔSPBC1198.07c	Anti-Longevity	Deletion mutation	Increase	GenAge database

• Comparative Phenotypic Analysis:

  • Assess resistance to various stressors (oxidative, heat, ER stress)

  • Analyze cell morphology and ultrastructure

  • Evaluate metabolic characteristics (respiration, glucose utilization)

Molecular Mechanisms Potentially Underlying Lifespan Extension:

• Altered Protein Quality Control:

  • Measure rates of protein synthesis and degradation

  • Assess accumulation of damaged or misfolded proteins

  • Analyze activity of proteostasis mechanisms (proteasome, autophagy)

• ER Stress and Unfolded Protein Response (UPR):

  • Monitor UPR activation using reporter constructs

  • Measure expression of ER chaperones (BiP/Grp78)

  • Analyze splicing of HAC1/IRE1 mRNA

• N-Glycan Structure and Processing:

  • Characterize glycan profiles in wild-type and mutant cells

  • Assess impact on specific glycoproteins

  • Investigate consequences for protein folding and trafficking

• Cell Wall Integrity and Composition:

  • Analyze cell wall structure and composition

  • Test sensitivity to cell wall-disrupting agents

  • Measure activation of cell wall integrity pathways

• Metabolic Alterations:

  • Perform metabolomic analysis to identify changed metabolites

  • Analyze energy metabolism and mitochondrial function

  • Investigate potential changes in nutrient sensing pathways

Understanding these mechanisms will not only provide insights into how SPBC1198.07c influences aging in S. pombe but may also reveal conserved pathways relevant to aging in other organisms, including humans.

What are the optimal strategies for expressing and purifying recombinant SPBC1198.07c protein?

Obtaining high-quality recombinant SPBC1198.07c protein is crucial for functional and structural studies. Based on published methods and protein characteristics, the following strategies are recommended:

Expression Systems and Conditions:

• E. coli Expression System:

  • Demonstrated success with His-tagged constructs

  • Recommended vectors: pET series with T7 promoter

  • Expression region: residues 25-507 (mature protein)

  • Induction conditions: IPTG at lower temperatures (25-30°C) to enhance solubility

  • Consider fusion partners (MBP, SUMO) to improve solubility if needed

• Baculovirus Expression System:

  • Shown to be effective for similar mannosidases

  • Advantages: proper protein folding, post-translational modifications

  • Use appropriate secretion signals for improved expression

• Yeast Expression System:

  • Consider P. pastoris for high-yield secreted expression

  • Particularly suitable for fungal proteins like SPBC1198.07c

  • Can provide native-like glycosylation

Purification Protocol:

• Affinity Chromatography:

  • Ni-NTA for His-tagged protein

  • Wash with low imidazole to remove non-specific binding

  • Elute with imidazole gradient (50-300 mM)

• Buffer Optimization:

  • Recommended storage buffer: Tris-based buffer with 50% glycerol

  • pH range: 7.5-8.0

  • Consider adding stabilizing agents (glycerol, reducing agents)

• Additional Purification Steps:

  • Size exclusion chromatography to remove aggregates

  • Ion exchange chromatography for removal of contaminants

  • Target purity: >85% by SDS-PAGE

Storage and Stability:

• Storage Conditions:

  • Store at -20°C or -80°C for extended storage

  • Use 50% glycerol as cryoprotectant

  • Avoid repeated freezing and thawing

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

• Stability Considerations:

  • Addition of protease inhibitors during purification

  • Consider adding divalent cations (Mn²⁺) that may stabilize the enzyme

  • Monitor activity over time to assess stability

Quality Control:

• Activity Assay:

  • Verify enzyme functionality using appropriate substrates

  • Compare specific activity to literature values for similar enzymes

• Biophysical Characterization:

  • Circular dichroism (CD) spectroscopy to assess secondary structure

  • Differential scanning fluorimetry (DSF) to measure thermal stability

  • Dynamic light scattering (DLS) to check for aggregation

These strategies should enable researchers to obtain pure, active SPBC1198.07c protein suitable for enzymatic, structural, and inhibitor studies.

How can researchers design experiments to investigate the role of SPBC1198.07c in ER stress and glycoprotein quality control?

Investigating the role of SPBC1198.07c in ER stress and glycoprotein quality control requires a multifaceted experimental approach:

Genetic Manipulation Strategies:

• Gene Deletion and Complementation:

  • Generate SPBC1198.07c deletion strains

  • Create complementation strains with wild-type or mutant versions

  • Develop strains with controlled expression (e.g., using thiamine-repressible promoters)

• Point Mutations:

  • Design catalytically inactive mutants (based on conserved active site residues)

  • Create mutations affecting localization or protein interactions

  • Verify effects of mutations on enzyme activity in vitro

ER Stress Induction and Analysis:

• Chemical ER Stress Inducers:

  • Tunicamycin: inhibits N-linked glycosylation

  • DTT: disrupts disulfide bonds

  • Thapsigargin: depletes ER calcium stores

• ER Stress Readouts:

  • Monitor BiP/Grp78 expression levels

  • Assess HAC1/IRE1 mRNA splicing

  • Measure activation of UPR-responsive promoters

  • Analyze phosphorylation of eIF2α

• Comparative Analysis:

  • Compare ER stress responses in wild-type vs. ΔSPBC1198.07c strains

  • Assess adaptive vs. terminal UPR activation

  • Evaluate cell survival under prolonged ER stress

Glycoprotein Processing and Quality Control:

• Glycan Analysis Techniques:

  • HPLC profiling of N-linked glycans

  • Mass spectrometry to determine detailed glycan structures

  • Lectin blotting to identify specific glycan epitopes

• Model Substrate Approach:

  • Express well-characterized glycoproteins (e.g., CPY*)

  • Monitor their processing, trafficking, and degradation

  • Compare glycosylation patterns in wild-type vs. mutant strains

• ERAD Pathway Analysis:

  • Measure rates of glycoprotein degradation using pulse-chase experiments

  • Analyze ubiquitination of ERAD substrates

  • Assess dependency on specific ERAD components

Cell Biological Approaches:

• Subcellular Localization:

  • Generate fluorescently tagged SPBC1198.07c

  • Perform co-localization with ER markers

  • Track changes in localization during ER stress

• Live Cell Imaging:

  • Monitor glycoprotein trafficking in real-time

  • Visualize ER morphology changes during stress

  • Assess protein aggregation in the ER

• Electron Microscopy:

  • Examine ER ultrastructure in wild-type vs. mutant cells

  • Use immunogold labeling to localize SPBC1198.07c

  • Identify morphological changes in the ER during stress

These experimental approaches will help elucidate the specific role of SPBC1198.07c in ER homeostasis, glycoprotein processing, and quality control mechanisms, potentially revealing new insights into the link between these processes and cellular aging.

What techniques can be used to study the interaction between SPBC1198.07c and other proteins in the mannan processing pathway?

Understanding the protein interaction network of SPBC1198.07c is crucial for elucidating its functional role within the mannan processing pathway. Multiple complementary techniques can be employed:

Biochemical and Biophysical Approaches:

• Affinity Purification-Mass Spectrometry (AP-MS):

  • Express tagged SPBC1198.07c in S. pombe

  • Purify protein complexes under native conditions

  • Identify interacting partners by LC-MS/MS

  • Quantify interactions using SILAC or TMT labeling

• Co-immunoprecipitation (Co-IP):

  • Generate antibodies against SPBC1198.07c or use tagged versions

  • Precipitate from native lysates under various conditions

  • Detect co-precipitated proteins by Western blotting

  • Verify interactions with suspected partners

• Surface Plasmon Resonance (SPR) or Bio-Layer Interferometry (BLI):

  • Use purified recombinant proteins

  • Determine binding kinetics and affinities

  • Characterize effects of mutations or inhibitors on interactions

• Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS):

  • Analyze oligomeric state of SPBC1198.07c alone and in complexes

  • Determine stoichiometry of protein complexes

  • Monitor complex formation under different conditions

Genetic and Cell-Based Approaches:

• Yeast Two-Hybrid (Y2H) Screening:

  • Use SPBC1198.07c as bait to identify interacting proteins

  • Perform directed Y2H with suspected partners

  • Map interaction domains through deletion analysis

• Genetic Interaction Analysis:

  • Screen for synthetic lethality/sickness with SPBC1198.07c deletion

  • Construct double mutants with other glycan processing enzymes

  • Analyze epistatic relationships

• Fluorescence-Based Interaction Assays:

  • Bimolecular Fluorescence Complementation (BiFC)

  • Förster Resonance Energy Transfer (FRET)

  • Fluorescence Correlation Spectroscopy (FCS)

  • Fluorescence Recovery After Photobleaching (FRAP)

• Proximity-Based Labeling:

  • BioID: Fuse SPBC1198.07c with a biotin ligase

  • APEX: Fuse with ascorbate peroxidase

  • Identify proximal proteins through biotinylation and purification

Structural Studies:

• X-ray Crystallography:

  • Crystallize SPBC1198.07c alone or in complex with partners

  • Determine atomic resolution structure

  • Identify interaction interfaces

• Cryo-Electron Microscopy:

  • Visualize larger protein complexes

  • Determine structure at near-atomic resolution

  • Analyze conformational changes upon complex formation

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Map protein-protein interaction interfaces

  • Detect conformational changes upon binding

  • Identify allosteric effects of interactions

A comprehensive analysis using multiple techniques will provide a detailed understanding of how SPBC1198.07c functions within the context of the mannan processing machinery and how these interactions contribute to glycoprotein processing and quality control in S. pombe.

What methodologies are appropriate for investigating the potential of SPBC1198.07c as an antifungal target?

Given the essential role of cell wall integrity and proper glycoprotein processing in fungal viability, SPBC1198.07c might represent a potential target for antifungal development. The following methodologies can be employed to evaluate its suitability:

Target Validation Studies:

• Phenotypic Characterization of Deletion Mutants:

  • Assess growth rates and morphology

  • Determine virulence in appropriate infection models

  • Evaluate fitness under various stress conditions

  • Test sensitivity to existing antifungals

• Conditional Expression Systems:

  • Create strains with regulated SPBC1198.07c expression

  • Determine the effects of gene repression on viability

  • Assess recovery after temporary repression

• Complementation Studies:

  • Express homologs from pathogenic fungi in S. pombe mutants

  • Determine functional conservation across species

  • Identify species-specific features that could be exploited

Inhibitor Discovery and Development:

• High-Throughput Screening:

  • Develop robust enzymatic assays suitable for screening

  • Screen chemical libraries for inhibitors

  • Validate hits using secondary assays

• Structure-Based Drug Design:

  • Use structural information (experimental or modeled)

  • Perform virtual screening campaigns

  • Design inhibitors targeting the active site or allosteric sites

• Fragment-Based Approaches:

  • Screen fragment libraries for binding to SPBC1198.07c

  • Develop fragments into lead compounds

  • This approach has been attempted with related mannosidases

Inhibitor Characterization:

• Enzymatic Inhibition Studies:

  • Determine IC50 and Ki values

  • Characterize inhibition mechanisms (competitive, non-competitive)

  • Assess selectivity against human homologs

• Cellular Activity Assessment:

  • Measure effects on fungal growth and viability

  • Analyze impact on cell wall composition

  • Evaluate morphological changes

• Resistance Development Studies:

  • Generate resistant mutants through laboratory evolution

  • Identify resistance mechanisms

  • Design strategies to overcome resistance

• Pharmacokinetic and Toxicity Studies:

  • Assess ADME properties of promising inhibitors

  • Evaluate cytotoxicity against mammalian cells

  • Determine in vivo efficacy in appropriate models

These methodologies will help determine whether SPBC1198.07c represents a viable target for antifungal development and could lead to the identification of novel compounds with activity against fungal pathogens.

How can researchers compare SPBC1198.07c function across different fungal species?

Comparative analysis of SPBC1198.07c across fungal species can provide evolutionary insights and potential species-specific therapeutic targets. The following methodologies are recommended:

Bioinformatic Analysis:

• Sequence-Based Approaches:

  • Perform BLAST searches against fungal genomes

  • Construct multiple sequence alignments

  • Build phylogenetic trees to visualize evolutionary relationships

  • Identify conserved domains and catalytic residues

• Comparative Genomics:

  • Analyze synteny around the gene across species

  • Identify species-specific gene duplications or losses

  • Compare promoter regions for regulatory elements

• Structural Prediction and Comparison:

  • Generate homology models for homologs from different species

  • Compare active site architecture

  • Identify species-specific structural features

Functional Characterization:

• Heterologous Expression Studies:

  • Express homologs from different fungal species in S. pombe ΔSPBC1198.07c strains

  • Test for functional complementation

  • Compare expression levels and localization patterns

• Biochemical Comparison:

  • Purify recombinant proteins from various fungal species

  • Compare enzymatic activities and substrate specificities

  • Analyze kinetic parameters and inhibitor sensitivities

  Species	Protein Name	Similarity to SPBC1198.07c	Key Differences
  S. cerevisiae	ER α-mannosidase	56.8% similarity	Different glycan processing pathway
  A. fumigatus	AnpA	Related α-1,6-mannosyltransferase	Involved in galactomannan synthesis

• Glycan Profiling:

  • Compare N-glycan structures across species

  • Identify species-specific glycan modifications

  • Correlate differences with enzyme specificities

Physiological Roles:

• Phenotypic Analysis of Mutants:

  • Create deletion mutants in multiple fungal species

  • Compare growth, morphology, and stress resistance

  • Assess effects on cell wall composition and integrity

• Specialized Functions:

  • Investigate role in pathogenesis for pathogenic species

  • Analyze contribution to stress responses

  • Assess involvement in developmental processes

• Interaction Networks:

  • Compare protein interaction partners across species

  • Identify conserved and species-specific interactions

  • Analyze differences in regulatory networks

These comparative approaches will provide insights into the evolution of mannan processing enzymes across fungi and may reveal species-specific features that could be exploited for the development of selective antifungal agents or for understanding fundamental aspects of fungal biology.