Recombinant Rhizobium sp. Uncharacterized protein y4lN (NGR_a02620)

How does y4lN compare to other characterized proteins in Rhizobium species?

While y4lN lacks direct functional characterization, comparative analysis places it in context with other Rhizobium proteins:

• Unlike the well-studied nodulation and nitrogen fixation genes (nif and fix), which comprise only 27 annotated genes in R. leguminosarum, y4lN belongs to the larger pool of genes potentially involved in symbiosis .

• Its classification as an "uncharacterized protein" distinguishes it from proteins with defined roles like the oxygen sensor proteins (hFixL, FnrN, and NifA) that regulate symbiotic gene expression .

• It does not appear to be among the well-characterized outer membrane proteins like RopB, which undergoes structural changes during bacteroid maturation .

Given that successful symbiosis requires genes for motility, cell envelope restructuring, nodulation signaling, nitrogen fixation, and metabolic adaptation , experimental studies would need to determine if y4lN functions in any of these processes.

What experimental approaches should be prioritized to characterize y4lN function?

A systematic approach to characterizing y4lN should include:

• Gene expression analysis: Determine if y4lN expression changes during different stages of symbiosis using qRT-PCR or RNA-seq, similar to studies of oxygen-regulated genes like fixNOQP .

• Knockout studies: Generate a y4lN deletion mutant and assess phenotypic changes in:

  • Free-living growth

  • Rhizosphere colonization

  • Root infection

  • Nodule formation

  • Nitrogen fixation efficiency (via acetylene reduction assays)

• Protein localization: Determine subcellular localization using fractionation techniques and immunodetection to establish if it's an outer membrane, inner membrane, or cytoplasmic protein.

• Interaction studies: Identify potential protein-protein interactions using pull-down assays with the available His-tagged recombinant protein .

• Comparative genomics: Analyze the distribution of y4lN homologs across rhizobial species and correlate with symbiotic capabilities.

This approach parallels the comprehensive methods used to characterize the oxygen regulation pathway in R. leguminosarum, where gene expression was measured in both free-living bacteria and bacteroids under various conditions .

What expression systems yield optimal results for recombinant y4lN production?

Based on available product information, recombinant y4lN has been successfully expressed in E. coli with an N-terminal His-tag . To optimize expression for research purposes:

• Expression vectors: pET-series vectors with the T7 promoter system are recommended for high-level bacterial protein expression.

• Host strains: BL21(DE3) or derivatives like Rosetta for codon optimization.

• Induction conditions: Optimize using Design of Experiments (DoE) methodology to systematically vary:

  • IPTG concentration

  • Temperature

  • Induction time

  • Media composition

DoE approaches for protein production enable efficient optimization with a minimum number of experiments, as shown in search result , which outlines how to create a cube representing the experimental space with different factors (e.g., pH, conductivity, temperature) on each axis.

For challenging proteins requiring post-translational modifications, alternative expression systems might be considered:

• Yeast systems for best yields with reasonable turnaround times

• Insect or mammalian cells for complex post-translational modifications

What is the optimal purification protocol for His-tagged y4lN protein?

For high-purity recombinant y4lN protein with an N-terminal His-tag:

• Initial capture: Immobilized metal affinity chromatography (IMAC) using Ni-NTA resin

  • Binding buffer: 20-50 mM imidazole to reduce non-specific binding

  • Elution: 250-500 mM imidazole gradient

• Intermediate purification: Size exclusion chromatography to:

  • Remove aggregates

  • Separate monomeric protein

  • Exchange into storage buffer

• Quality control:

  • SDS-PAGE (should show >90% purity as specified in product information)

  • Mass spectrometry for identity confirmation

  • Dynamic light scattering for homogeneity assessment

• Storage preparation:

  • Buffer exchange into Tris-based buffer, pH 8.0 with 6% trehalose or 50% glycerol

  • Aliquoting to avoid freeze-thaw cycles

  • Flash freezing in liquid nitrogen before storage at -20°C/-80°C

The complete amino acid sequence should be verified to ensure integrity: MISEASSRPGFITAPADPVGEYPRASRRFESALLHIEVLSAMNIEKLLGGFANVAAILTP LVAVLAYSRFLWERRQKRLRLESYLREQKLFECTGQHSFLHLVATLGMFEADIMDASYRS KVISRNVAVDVAGEPVRIVLEYEPDDLEKELPKRPGRGQF .

How can researchers verify proper folding of recombinant y4lN?

Verifying proper folding of an uncharacterized protein presents unique challenges. A multi-technique approach is recommended:

• Biophysical characterization:

  • Circular dichroism (CD) spectroscopy to assess secondary structure

  • Differential scanning fluorimetry (DSF) to determine thermal stability

  • Size exclusion chromatography with multi-angle light scattering (SEC-MALS) to confirm monodispersity

• Limited proteolysis:

  • Treatment with proteases like trypsin or chymotrypsin

  • Well-folded proteins show resistance to proteolysis except at exposed loops

  • Analysis of digestion patterns by SDS-PAGE or mass spectrometry

• Structural homology modeling:

  • Use of AlphaFold2 or similar tools to predict structure

  • Experimental verification of key structural features predicted by the model

• Activity surrogate assays:

  • Lipid binding assays if membrane association is predicted

  • Interactions with known Rhizobium outer membrane proteins

Researchers should avoid repeated freeze-thaw cycles as mentioned in the product information, as this can lead to protein denaturation and aggregation .

Could y4lN be involved in Rhizobium-legume symbiosis?

While direct evidence for y4lN's role in symbiosis is lacking, several factors suggest it may be involved:

• Genomic context: The protein is found in Rhizobium sp. strain NGR234, which forms symbiotic relationships with legumes.

• Potential membrane association: If y4lN is an outer membrane protein, it could participate in plant-microbe interactions, similar to other OMPs involved in symbiosis .

• Research framework: Studies have shown that 603 genetic regions in Rhizobium leguminosarum are required for competitive nodulation and nitrogen fixation, far beyond the 27 annotated nif and fix genes .

To investigate y4lN's potential role in symbiosis, researchers should:

• Analyze gene expression across different symbiotic stages (free-living, rhizosphere colonization, infection, bacteroid formation)

• Generate a knockout mutant and assess its ability to:

  • Compete in the rhizosphere (potentially among the 17 genes specific for rhizosphere growth)

  • Colonize roots (potentially among the 23 genes for root colonization)

  • Form infection threads

  • Differentiate into bacteroids

  • Fix nitrogen (measured by acetylene reduction assays as shown in Figure 5A from search result )

• Compare expression under different oxygen conditions, as oxygen concentration is a key regulator of symbiotic genes, with different sensors active at 1% O₂ versus near-anaerobic conditions .

Could y4lN interact with legume host proteins?

Recent research has identified direct protein-protein interactions between rhizobial outer membrane proteins and host legume proteins:

• A germin-like protein GLP1 from legumes has been shown to interact with the outer membrane protein Mhopa22 from Mesorhizobium huakuii, mediating symbiotic nodulation .

• This represents the first characterized legume host plant protein that senses and interacts with a rhizobial outer membrane protein .

• Homologous genes to the OMP identified (Mhopa22) are widely distributed in Rhizobiales .

To investigate if y4lN similarly interacts with legume proteins:

• Pull-down assays using His-tagged recombinant y4lN with plant root extracts

• Yeast two-hybrid screening against a library of legume proteins

• Surface plasmon resonance (SPR) to measure binding kinetics with candidate plant proteins

• Co-immunoprecipitation from nodule extracts using antibodies against y4lN

This approach parallels the methods used to identify the GLP1-Mhopa22 interaction, which revealed that this interaction plays an essential role in mediating early symbiotic processes .

How would oxygen concentration affect y4lN expression in nodules?

Oxygen regulation is critical for symbiotic gene expression in rhizobia. In R. leguminosarum, three oxygen sensors (hFixL, FnrN, and NifA) function at different oxygen concentrations to regulate gene expression during nodule development :

To determine if y4lN is subject to oxygen regulation:

• Measure gene expression:

  • At different oxygen concentrations (21%, 1%, 0.1%, <0.01%)

  • In different nodule zones using laser capture microdissection

  • Using reporter gene fusions (promoter-GFP)

• Analyze the promoter region for binding sites of known oxygen-responsive regulators:

  • FnrN binding sites

  • FixK binding sites

• Compare expression patterns with known oxygen-regulated genes like fixNOQP, which show different expression patterns in wild-type bacteria versus fnrN or hfixL mutants .

This approach would determine if y4lN belongs to the oxygen-regulated gene set essential for nitrogen fixation in nodules, providing important functional context.

What mutagenesis strategies are most effective for studying y4lN function?

A comprehensive mutagenesis approach should include:

• Complete gene deletion:

  • Create an in-frame deletion using homologous recombination

  • Assess phenotypes in free-living and symbiotic conditions

  • Compare to wild-type in competitive nodulation assays

• Domain-targeted mutagenesis:

  • Identify potential functional domains through sequence analysis

  • Create targeted mutations or truncations

  • Express mutant versions in the knockout background

• Site-directed mutagenesis:

  • Target conserved residues identified through comparative analysis

  • Focus on predicted functional sites (membrane-interacting regions)

  • Generate alanine-scanning libraries of charged/aromatic residues

• Complementation testing:

  • Reintroduce wild-type or mutant versions into knockout strain

  • Quantify restoration of phenotypes (growth, nodulation, nitrogen fixation)

This approach is similar to the genetic analysis of oxygen sensing in R. leguminosarum, where mutations in fnrN reduced nitrogen fixation by 85%, while mutations in hfixL reduced it by only 25% .

For analysis of nodulation phenotypes, researchers should quantify:

• Number of nodules

• Nodule morphology and color

• Expression of symbiotic genes using reporter fusions

• Nitrogen fixation using acetylene reduction assays

How can comparative genomics inform y4lN function?

Comparative genomic approaches can provide significant insights:

• Homolog identification:

  • BLASTP searches against rhizobial and related bacterial genomes

  • Identification of conserved domains and motifs

  • Analysis of genomic context conservation

• Synteny analysis:

  • Examine gene neighborhoods across species

  • Identify conserved operons or gene clusters

• Phylogenetic analysis:

  • Construct phylogenetic trees using ClustalW and NJplot as described for OMP analysis

  • Map symbiotic properties onto the phylogeny

  • Identify correlation with host specificity

• Correlation with experimental data:

  • Compare with transposon mutagenesis data to identify functional categories

  • Map onto nodule zone-specific expression data

This approach can place y4lN in the context of the 603 genetic regions required for competitive nodulation and nitrogen fixation, potentially identifying it as part of the 146 "rhizosphere-progressive" genes common to multiple stages or among the 211 genes specific for nodule bacteria and bacteroid function .

What approaches can determine if y4lN is involved in rhizobial competition?

Competition in the rhizosphere is critical for successful symbiosis. To assess y4lN's potential role:

• Competitive nodulation assays:

  • Co-inoculate wild-type and y4lN mutant strains in different ratios

  • Identify strain occupancy in nodules using specific markers

  • Calculate competitive indices

• Rhizosphere colonization dynamics:

  • Monitor populations of wild-type and mutant strains over time

  • Use fluorescent protein markers for microscopic tracking

  • Quantify by dilution plating on selective media

• Root attachment assays:

  • Compare biofilm formation on root surfaces

  • Measure early colonization efficiency

  • Evaluate resistance to displacement

• Transcriptomic comparison:

  • Compare gene expression changes in wild-type vs. mutant

  • Focus on conditions mimicking rhizosphere environment

  • Identify downstream pathways affected by y4lN mutation

This approach aligns with findings that successful competition in the rhizosphere is critical to subsequent infection and nodulation, with 146 genes classified as "rhizosphere-progressive" being common to multiple stages of symbiosis .

What computational approaches can predict y4lN structure and function?

For an uncharacterized protein like y4lN, computational approaches offer valuable structural insights:

• Sequence-based predictions:

  • Secondary structure prediction (α-helices, β-sheets)

  • Transmembrane region identification

  • Disorder prediction

  • Functional domain recognition

• Ab initio structure prediction:

  • AlphaFold2 modeling for tertiary structure

  • Rosetta for generating alternative conformations

  • Molecular dynamics simulations to assess stability

• Functional prediction:

  • Binding site identification

  • Electrostatic surface analysis

  • Structural comparison with characterized proteins

• Genomic context analysis:

  • Co-expression with functionally characterized genes

  • Presence in conserved operons

  • Correlation with symbiotic phenotypes

These computational predictions should guide experimental design, including selection of residues for mutagenesis and design of protein interaction studies.

How can researchers analyze potential post-translational modifications of y4lN?

Analysis of post-translational modifications (PTMs) in y4lN requires:

• Mass spectrometry approaches:

  • LC-MS/MS analysis of tryptic peptides

  • Multiple fragmentation methods (CID, ETD, HCD)

  • Precursor ion scanning for specific modifications

• Specific modification analyses:

  • Phosphorylation: Phos-tag SDS-PAGE, 32P-labeling

  • Glycosylation: Periodic acid-Schiff staining, lectin blotting

  • Lipidation: Metabolic labeling with fatty acid analogs

• Comparative PTM profiling:

  • Free-living vs. symbiotic states

  • Different oxygen conditions

  • Various plant hosts

• Functional validation:

  • Site-directed mutagenesis of modified residues

  • Phenotypic analysis of modification-deficient mutants

While the recombinant protein expressed in E. coli may lack eukaryotic-type modifications, bacterial-specific modifications are still possible and potentially important for function.

What techniques are most effective for identifying y4lN protein interactions?

To identify protein interaction partners of y4lN:

• Pull-down assays using His-tagged recombinant protein:

  • Immobilize purified y4lN on Ni-NTA resin

  • Incubate with cellular extracts from:

    • Free-living rhizobia

    • Bacteroids isolated from nodules

    • Plant root extracts

  • Identify binding partners by mass spectrometry

• Crosslinking-mass spectrometry:

  • Chemical crosslinking of intact cells

  • Isolation of y4lN-containing complexes

  • MS/MS analysis to identify crosslinked peptides

• Bacterial two-hybrid systems:

  • Particularly useful for membrane proteins

  • Screen against genomic libraries

• Surface plasmon resonance (SPR):

  • Quantitative measurement of binding kinetics

  • Test interactions with purified candidate proteins

These approaches could reveal if y4lN interacts with plant proteins similar to the interaction between the rhizobial outer membrane protein Mhopa22 and the legume GLP1 protein reported in recent research .

Could y4lN be involved in ascending colonization of plants by Rhizobium?

Rhizobia can form endophytic associations with non-legume plants and migrate from roots to above-ground tissues. To investigate y4lN's potential role:

• Colonization tracking experiments:

  • Inoculate plant roots with GFP-tagged wild-type and y4lN mutant strains

  • Monitor bacterial migration to above-ground tissues using confocal microscopy

  • Quantify colonization at different time points by viable plating

• Tissue-specific expression analysis:

  • Measure y4lN expression in bacteria isolated from different plant tissues

  • Compare expression patterns between root-associated and stem/leaf-associated bacteria

• Plant response comparison:

  • Analyze transcriptomic differences in plants colonized by wild-type vs. y4lN mutant

  • Focus on defense and colonization-related genes

This approach parallels the methods used to study ascending migration of endophytic rhizobia from roots to leaves, where computer-assisted microscopy and viable plating methods quantified colonization and dispersion in rice plants .

How might y4lN contribute to heavy metal stress responses in plant-Rhizobium symbiosis?

Recent research shows Rhizobium symbiosis improves amino acid and secondary metabolite profiles in tungsten-stressed soybean plants . To investigate if y4lN contributes to metal stress responses:

• Comparative stress experiments:

  • Expose plants inoculated with wild-type vs. y4lN mutant to heavy metals

  • Measure plant growth parameters and stress indicators

  • Analyze metal uptake and translocation

• Metabolomic analysis:

  • Compare metabolite profiles in plants colonized by wild-type vs. mutant

  • Focus on protective compounds like phenols, polyamines, gluconic acid, and proline

  • Measure antioxidant capacity

• Bacterial survival assays:

  • Test sensitivity of y4lN mutant to heavy metals

  • Measure expression changes of y4lN under metal stress

  • Evaluate metal binding capacity of recombinant y4lN

This approach builds on findings that symbiotically grown plants (N fix) significantly increase synthesis of protective compounds compared to non-symbiotic counterparts (N fed) under tungsten stress .

Could understanding y4lN function lead to improved agricultural applications?

Practical agricultural applications from y4lN research might include:

• Enhanced inoculant development:

  • If y4lN proves important for competitive nodulation, strains with optimized expression could be developed

  • Genetic engineering of commercial inoculants to improve symbiotic efficiency

• Non-legume crop applications:

  • If y4lN plays a role in endophytic colonization of cereals, it could be targeted for engineering improved plant-microbe associations

  • Development of rhizobial strains with enhanced colonization abilities for non-legume crops

• Stress tolerance improvement:

  • If y4lN contributes to heavy metal tolerance, it could be used to develop inoculants for contaminated soils

  • Engineering strains with enhanced expression for specific stress conditions

• Monitoring tools:

  • Development of y4lN-based biosensors to monitor soil conditions

  • Use as a marker for tracking rhizobial persistence in field conditions

The potential applications align with recent research showing how plant-microbe interactions and plant growth promotion by rhizobacteria can contribute to sustainable and robust agroecosystems .

What databases and tools are most useful for y4lN research?

Researchers studying y4lN should utilize:

• Sequence databases and analysis tools:

  • RhizoBase (http://bacteria.kazusa.or.jp/rhizobase/) for rhizobial genomes and comparative analysis

  • BLASTP for homology searches and identification of conserved domains

  • ClustalW for multiple sequence alignments

  • NJplot for constructing phylogenetic trees

• Structural analysis tools:

  • AlphaFold2 for structure prediction

  • PyMOL or Chimera for structural visualization

  • ConSurf for evolutionary conservation mapping

• Functional annotation resources:

  • Gene ontology databases

  • Protein family databases (Pfam, InterPro)

  • Metabolic pathway databases (KEGG, MetaCyc)

• Expression data repositories:

  • Transcriptomic datasets from different symbiotic conditions

  • RNA-seq data from nodule zone-specific studies

These resources can help place y4lN in the context of other symbiosis-related proteins and guide experimental approaches.

What is the optimal storage protocol for recombinant y4lN protein?

Based on product information for recombinant y4lN :

• Long-term storage:

  • Store at -20°C/-80°C

  • Keep as lyophilized powder or in buffer with 50% glycerol

  • Avoid repeated freeze-thaw cycles

• Reconstitution of lyophilized protein:

  • Briefly centrifuge vial before opening

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

  • Add glycerol to 5-50% final concentration for aliquoting

• Working solutions:

  • Store at 4°C for up to one week

  • Use Tris/PBS-based buffer, pH 8.0 with 6% trehalose

  • Keep on ice during experiments

• Quality monitoring:

  • Periodically check protein integrity by SDS-PAGE

  • Monitor activity/folding using appropriate assays

  • Check for aggregation using dynamic light scattering

Following these guidelines will ensure the protein maintains its native structure and potential activity for experimental use.

What controls are essential in functional studies of y4lN?

Rigorous controls for y4lN functional studies should include:

• Genetic controls:

  • Empty vector control for expression studies

  • Complemented mutant strain (wild-type gene reintroduced into knockout)

  • Point mutant controls for specific functional hypotheses

• Protein interaction controls:

  • Unrelated His-tagged protein for pull-down specificity

  • Pre-immune serum for immunoprecipitation

  • Heat-denatured protein control

• Expression analysis controls:

  • Multiple reference genes for qRT-PCR normalization

  • Samples from different growth phases and conditions

  • Positive control genes known to be regulated in similar patterns

• Phenotypic assay controls:

  • Wild-type strain in all experiments

  • Known mutants with established phenotypes

  • Mixed inoculation experiments with differentially marked strains