Recombinant Aliivibrio salmonicida tRNA dimethylallyltransferase (miaA)

What is tRNA dimethylallyltransferase (miaA) and what is its function?

tRNA dimethylallyltransferase (miaA) is an enzyme that catalyzes the transfer of a dimethylallyl group onto the adenine at position 37 in tRNAs that read codons beginning with uridine. This reaction leads to the formation of N6-(dimethylallyl)adenosine (i6A) . The enzyme belongs to the IPP transferase family and plays a crucial role in tRNA modification, which affects translation efficiency and fidelity. This post-transcriptional modification helps stabilize codon-anticodon interactions during protein synthesis, particularly for tRNAs that recognize codons beginning with U.

What is the structural composition of Aliivibrio salmonicida miaA?

While the search results don't provide the exact structure for Aliivibrio salmonicida miaA, we can draw parallels from related bacterial species. The miaA protein typically consists of approximately 290-310 amino acids, as seen in Aeromonas salmonicida (310 amino acids) and Streptococcus suis (294 amino acids) . The protein contains conserved domains characteristic of the IPP transferase family, including nucleotide-binding regions and catalytic sites necessary for its enzymatic function.

How does miaA protein expression differ between various bacterial species?

Based on available sequence data, miaA proteins from different bacterial species share conserved functional domains but display sequence variability. For example, Aeromonas salmonicida miaA has the sequence beginning with "MNVTDLPNAI FLMGPTASGK..." , while Streptococcus suis miaA begins with "MKTKVIVVIGPTAVGK..." . This sequence variation likely reflects evolutionary adaptations to different bacterial physiologies while maintaining the core enzymatic function. Comparative sequence analysis reveals that the catalytic core and substrate binding regions tend to be more conserved than other portions of the protein.

What are the optimal conditions for recombinant expression of Aliivibrio salmonicida miaA?

For optimal recombinant expression of miaA proteins, researchers typically use E. coli expression systems with vectors such as pET-29a, which can add a 6xHis tag for purification purposes . Expression is commonly induced using IPTG (1 mM) when cultures reach an OD600 of 0.6, with induction occurring at 37°C for 3 hours . For miaA specifically, codon optimization for E. coli expression may improve yields, as was done for other bacterial proteins . It may be beneficial to test different expression temperatures (16°C, 25°C, and 37°C) and induction times to optimize soluble protein production.

What purification strategies yield the highest purity for recombinant miaA?

Nickel-chelated immobilized metal affinity chromatography (IMAC) is the preferred method for purifying His-tagged recombinant miaA proteins . The detailed purification protocol involves:

• Cell lysis using a French Press at 27 Kpsi in appropriate buffer (50 mM Tris-HCl, 500 mM NaCl, pH 9.0)

• Clarification of lysate by centrifugation (32,000 rpm at 4°C for 45 min)

• Solubilization of inclusion bodies with 6M urea if the protein is insoluble

• Filtration through a 0.22 μm membrane before loading onto IMAC resin

• Washing with column buffer (50 mM Sodium phosphate pH 7.4, 500 mM NaCl, 5 mM imidazole)

• Elution using a 250-500 mM linear imidazole gradient

• Analysis of fractions by SDS-PAGE, pooling of pure fractions

• Dialysis against PBS to remove imidazole

This method typically yields protein with >85% purity as assessed by SDS-PAGE .

How can I determine the purity and activity of purified recombinant miaA?

The purity of recombinant miaA can be assessed using SDS-PAGE, with commercial preparations typically achieving >85% purity . For activity assessment, researchers should consider:

• Enzymatic assays measuring the transfer of dimethylallyl groups to tRNA substrates

• Mass spectrometry to confirm post-translational modifications

• Circular dichroism to verify proper protein folding

• Size-exclusion chromatography to assess protein aggregation

• Thermal shift assays to evaluate protein stability

For quantitative activity measurement, radioactive assays using [14C]-dimethylallyl pyrophosphate can track the transfer to tRNA substrates, though non-radioactive HPLC-based methods are increasingly preferred.

What are the optimal storage conditions for maintaining miaA stability and activity?

For optimal storage of recombinant miaA protein, the following conditions are recommended:

• Store at -20°C for short-term storage

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

• Add glycerol (5-50% final concentration) to prevent freeze-thaw damage, with 50% being standard for many commercial preparations

• Aliquot the protein solution to avoid repeated freeze-thaw cycles

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

The shelf life of liquid preparations is typically 6 months at -20°C/-80°C, while lyophilized forms can maintain stability for 12 months at the same temperatures .

How does freeze-thaw cycling affect miaA activity and structural integrity?

Repeated freezing and thawing is not recommended for miaA proteins as it can lead to protein denaturation, aggregation, and loss of enzymatic activity . Each freeze-thaw cycle can cause partial unfolding of the protein structure, exposing hydrophobic regions that promote aggregation. Additionally, ice crystal formation during freezing can cause mechanical stress on the protein structure. To minimize these effects:

• Divide the protein solution into single-use aliquots

• Add cryoprotectants like glycerol (recommend 50% final concentration)

• Use rapid freezing techniques (liquid nitrogen) when possible

• Allow protein to thaw completely at 4°C before use

• Avoid vortexing, which can cause protein denaturation through mechanical stress

How can I design experiments to assess the impact of miaA mutations on tRNA modification efficiency?

To investigate how mutations in miaA affect tRNA modification, consider this experimental design:

• Generate site-directed mutants targeting:

  • Conserved catalytic residues

  • Substrate binding sites

  • Regulatory domains

• Express and purify wild-type and mutant proteins using standardized methods

• Assess enzymatic activity using:

  • In vitro assays with purified tRNA substrates

  • LC-MS/MS analysis to quantify modified nucleosides

  • Kinetic measurements to determine changes in Km and Vmax

• Complement with structural analysis:

  • Circular dichroism to detect conformational changes

  • Thermal shift assays to measure protein stability

  • Computational modeling to predict mutation effects

• In vivo validation:

  • Complementation studies in miaA knockout strains

  • Growth phenotype analysis under various stress conditions

  • Ribosome profiling to assess translation effects

This approach will provide comprehensive insights into structure-function relationships of miaA mutations.

What techniques are most effective for studying miaA-tRNA interactions?

For studying miaA-tRNA interactions, researchers should consider the following techniques:

A combination of these methods provides the most comprehensive understanding of miaA-tRNA interactions at molecular resolution.

How does miaA activity correlate with bacterial stress response and antibiotic resistance?

While direct evidence for Aliivibrio salmonicida miaA is limited in the search results, research on related bacterial species suggests that tRNA modifications catalyzed by miaA play important roles in stress response and potentially antibiotic resistance. To investigate these correlations, researchers should:

• Generate miaA knockout and overexpression strains to compare:

  • Growth rates under various stress conditions (temperature, pH, oxidative stress)

  • Minimum inhibitory concentrations (MICs) for different antibiotic classes

  • Transcriptomic and proteomic profiles under stress conditions

• Analyze tRNA modification levels using:

  • LC-MS/MS to quantify i6A levels in different growth conditions

  • Codon-specific translation efficiency through ribosome profiling

  • Mistranslation rates using reporter systems

• Assess physiological impacts through:

  • Biofilm formation capacity

  • Virulence in infection models

  • Metabolic adaptations through metabolomic analysis

Understanding these correlations could potentially identify miaA as a novel target for antimicrobial development, particularly against Aliivibrio salmonicida infections in aquaculture.

How conserved is miaA across different bacterial species and what can this tell us about its evolutionary importance?

Analysis of miaA sequences from different bacterial species, including Aeromonas salmonicida and Streptococcus suis , reveals significant conservation of catalytic and substrate-binding domains. This conservation suggests that tRNA modification by miaA represents an evolutionarily ancient and fundamental process in bacterial physiology.

To assess evolutionary conservation:

• Perform phylogenetic analysis of miaA sequences across diverse bacterial phyla

• Map conserved residues to structural models to identify functional constraints

• Compare enzymatic properties from distantly related bacteria

• Correlate miaA presence/absence with ecological niches and lifestyle adaptations

• Analyze codon usage patterns in relation to tRNA modifications across species

The high conservation of miaA across bacterial species underscores its fundamental role in translation accuracy and efficiency, particularly for codons beginning with uridine that benefit from the stabilizing effect of i6A modification.

What structural differences exist between miaA from Aliivibrio salmonicida and other bacterial species?

While specific structural information for Aliivibrio salmonicida miaA is not provided in the search results, we can draw insights from comparing available sequences of related bacterial miaA proteins. Key points for structural comparison include:

• Sequence alignment between Aeromonas salmonicida miaA (310 amino acids) and Streptococcus suis miaA (294 amino acids) shows distinct differences in N-terminal regions while maintaining conserved catalytic domains.

• Predicted structural features to analyze include:

  • Nucleotide binding domains (GXGXXG motifs)

  • Dimethylallyl pyrophosphate binding sites

  • tRNA recognition elements

  • Species-specific insertions or deletions

• Functional implications of these structural differences may include:

  • Substrate specificity variations

  • Regulatory mechanism adaptations

  • Environmental condition responses

  • Protein-protein interaction capabilities

Researchers should use computational modeling and experimental structure determination methods like X-ray crystallography or cryo-EM to fully characterize these differences.

What strategies can resolve poor expression yields of recombinant miaA?

When facing poor expression yields of recombinant miaA, researchers should systematically troubleshoot using these approaches:

• Vector optimization:

  • Try different expression vectors (pET systems, pGEX, etc.)

  • Optimize promoter strength for the specific protein

  • Consider adding solubility tags (MBP, SUMO, etc.)

• Host strain selection:

  • Test expression in different E. coli strains (BL21(DE3), Rosetta, Arctic Express)

  • Consider specialized strains for toxic or membrane proteins

  • Evaluate strains with extra tRNAs for rare codons

• Expression condition optimization:

  • Reduce temperature to 16-25°C during induction

  • Decrease IPTG concentration (0.1-0.5 mM)

  • Extend induction time (overnight at lower temperatures)

  • Try autoinduction media for gradual protein expression

• Genetic optimization:

  • Codon optimization for E. coli expression

  • Remove problematic secondary structures in mRNA

  • Consider expressing truncated functional domains if full-length is problematic

• Solubility enhancement:

  • Add osmolytes or stabilizing agents to the culture medium

  • Co-express with chaperones (GroEL/ES, DnaK)

  • Try fusion partners known to enhance solubility

Implementation of these strategies in a systematic manner can significantly improve recombinant miaA yields.

How can I troubleshoot issues with miaA enzymatic activity assays?

When enzymatic activity assays for miaA yield inconsistent or negative results, consider the following troubleshooting approach:

• Protein quality issues:

  • Verify protein folding using circular dichroism

  • Check for aggregation using size exclusion chromatography

  • Ensure complete removal of denaturing agents after purification

  • Test different storage buffers and conditions

• Substrate considerations:

  • Ensure tRNA substrates are properly folded

  • Use freshly prepared dimethylallyl pyrophosphate

  • Verify substrate purity by gel electrophoresis or HPLC

  • Try tRNAs from different sources (synthetic vs. native)

• Reaction conditions optimization:

  • Systematically vary pH (6.5-8.5)

  • Test different divalent cation concentrations (Mg2+, Mn2+)

  • Optimize temperature (25-37°C)

  • Adjust enzyme:substrate ratios

• Detection method validation:

  • Include appropriate positive and negative controls

  • Validate assay sensitivity with known standards

  • Consider alternative detection methods (radioactive, fluorescent, LC-MS)

  • Ensure analysis conditions don't interfere with detection

• Inhibitory factors:

  • Test for inhibitory contaminants from purification

  • Remove potential chelating agents from buffers

  • Check for product inhibition effects

  • Minimize oxidation by adding reducing agents

Methodical investigation of these factors will help identify and resolve issues with enzymatic assays.

How might miaA be utilized as a potential vaccine candidate against bacterial infections?

Recent research in reverse vaccinology has identified outer membrane proteins as promising vaccine candidates against bacterial infections . While miaA itself is not mentioned specifically as a vaccine candidate in the search results, the approaches used for other bacterial proteins provide a framework for evaluating miaA's potential:

• Assessment criteria for miaA as vaccine candidate:

  • Surface accessibility and exposure to host immune system

  • Conservation across virulent strains

  • Role in bacterial virulence and pathogenesis

  • Immunogenicity and ability to elicit protective responses

• Experimental approach:

  • Generate recombinant miaA using established expression protocols

  • Assess immunogenicity in animal models with measurement of antibody titers

  • Evaluate protective efficacy in challenge models

  • Consider combination with other antigens for synergistic protection

• Advantages of enzyme-based vaccines:

  • Potential to target conserved catalytic domains

  • Opportunity to disrupt essential bacterial processes

  • Possible cross-protection against multiple species with conserved miaA

• Challenges to address:

  • Limited surface accessibility of cytoplasmic enzymes

  • Potential cross-reactivity with host proteins

  • Need for appropriate adjuvants to enhance immunogenicity

  • Demonstration of protection in relevant animal models

The reverse vaccinology approach that successfully identified other bacterial antigens could be applied to evaluate miaA's potential as a component of multi-subunit vaccines .

What are the latest discoveries regarding the role of miaA in bacterial pathogenesis?

While the search results don't provide specific information on miaA's role in Aliivibrio salmonicida pathogenesis, research on related bacterial systems suggests several potential mechanisms by which miaA could influence virulence:

• Translation efficiency regulation:

  • Modification of tRNAs by miaA affects translation of specific codons

  • This can alter expression of virulence factors requiring these codons

  • Stress response proteins often contain codon biases that depend on modified tRNAs

• Stress adaptation:

  • tRNA modifications may help bacteria adapt to host environments

  • Changes in temperature, pH, and nutrient availability in host tissues

  • Modified tRNAs potentially stabilize translation under stress conditions

• Regulatory roles:

  • tRNA-modifying enzymes may have moonlighting functions

  • Possible interactions with regulatory proteins or nucleic acids

  • Potential involvement in biofilm formation

• Host-pathogen interactions:

  • Modified tRNAs could influence expression of surface antigens

  • Impact on secretion systems and effector molecules

  • Potential recognition by host immune receptors

Future research should investigate these aspects specifically in Aliivibrio salmonicida to understand miaA's contribution to fish pathogenesis in aquaculture settings.

How might CRISPR-Cas9 technology be applied to study miaA function in bacterial systems?

CRISPR-Cas9 technology offers powerful approaches for studying miaA function in bacterial systems:

• Gene knockout and complementation:

  • Create precise miaA deletions with minimal polar effects

  • Complement with wild-type or mutant variants

  • Generate conditional knockouts using inducible promoters

• Base editing applications:

  • Introduce point mutations in catalytic domains

  • Create subtle modifications without disrupting gene context

  • Engineer regulatory element changes to alter expression

• CRISPRi approaches:

  • Tune down miaA expression without complete deletion

  • Study dosage effects on tRNA modification

  • Temporally control miaA expression to study dynamics

• CRISPR screens:

  • Create libraries targeting miaA interaction partners

  • Screen for synthetic lethality with miaA mutations

  • Identify compensatory pathways activated in miaA-deficient strains

• Multiomics integration:

  • Combine CRISPR manipulation with transcriptomics

  • Link to proteomics to study translation effects

  • Integrate with metabolomics to understand physiological impacts

Implementation of these CRISPR-based approaches would significantly advance our understanding of miaA's role in bacterial physiology and potentially identify novel antimicrobial targets.

What analytical methods are most sensitive for detecting and quantifying tRNA modifications catalyzed by miaA?

For detecting and quantifying N6-(dimethylallyl)adenosine (i6A) modifications in tRNA, researchers should consider these analytical methods:

For optimal results, LC-MS/MS is the gold standard, providing both high sensitivity and specificity for identifying and quantifying i6A modifications. Method selection should balance sensitivity requirements, available equipment, and experimental goals.

How can I establish a reliable in vitro assay system for measuring miaA enzymatic activity?

A robust in vitro assay system for measuring miaA enzymatic activity should include:

• Enzyme preparation:

  • Use freshly purified recombinant miaA (>85% purity)

  • Determine optimal enzyme concentration through titration

  • Ensure proper folding and stability in assay buffer

• Substrate preparation:

  • Generate unmodified tRNA substrates through in vitro transcription

  • Alternatively, isolate total tRNA from miaA-deficient strains

  • Verify tRNA quality by gel electrophoresis and spectrophotometry

• Assay components:

  • Reaction buffer: 50 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 100 mM KCl

  • Dimethylallyl pyrophosphate (DMAPP): 50-100 μM

  • tRNA substrate: 5-10 μM

  • Recombinant miaA: 0.1-1 μM

  • Reducing agent: 1-5 mM DTT or 2-mercaptoethanol

• Detection methods:

  • Direct measurement: LC-MS/MS quantification of modified tRNA

  • Indirect measurement: Pyrophosphate release assays

  • Radioactive assay: Using [14C]-DMAPP and measuring incorporation

• Controls and validation:

  • No-enzyme control to establish background

  • Heat-inactivated enzyme as negative control

  • Known concentrations of modified tRNA as standards

  • Time course to establish linear range of assay

• Analysis parameters:

  • Initial velocity conditions (<20% substrate conversion)

  • Michaelis-Menten kinetics determination (Km, Vmax)

  • Specificity constants (kcat/Km) for different tRNA substrates

This comprehensive approach will enable reliable quantification of miaA enzymatic activity for functional studies.

How does miaA activity integrate with other tRNA modification pathways in bacterial systems?

tRNA modification by miaA is part of an interconnected network of modifications that collectively influence bacterial translation and physiology:

• Sequential modification pathways:

  • miaA catalyzes the first step (i6A formation) in a pathway that can continue with MiaB (adding sulfur to form ms2i6A)

  • These modifications occur at position 37, adjacent to the anticodon

  • The presence of i6A can influence subsequent modifications at nearby positions

• Coordination with other modification systems:

  • Modifications at the anticodon loop (positions 34, 37, 38, 39)

  • Interactions with T-arm and D-arm modifications

  • Synergistic effects on tRNA structure and function

• Regulatory integration:

  • Environmental conditions may trigger coordinated changes in multiple tRNA modification enzymes

  • Stress responses can alter the modification profile of tRNAs

  • Translation efficiency and accuracy depend on the complete modification pattern

• Systems biology approaches to study integration:

  • Global analysis of modification patterns under different conditions

  • Correlation of modifications with transcriptome and proteome changes

  • Network modeling of modification enzyme interactions

• Experimental strategies:

  • Multi-omics integration (epitranscriptomics, proteomics, metabolomics)

  • Creation of multiple modification enzyme mutants

  • Global translation efficiency measurement using ribosome profiling

Understanding these integrated networks is essential for comprehending how miaA contributes to bacterial adaptation and pathogenesis in diverse environments.

What bioinformatic tools are most useful for analyzing miaA genes across bacterial genomes?

For comprehensive analysis of miaA genes across bacterial genomes, researchers should utilize these bioinformatic tools:

• Sequence identification and annotation:

  • BLAST/PSI-BLAST: Identify miaA homologs across genomes

  • InterProScan: Annotate functional domains and motifs

  • Pfam: Classify proteins into IPP transferase family

• Phylogenetic analysis:

  • MEGA: Construct phylogenetic trees to trace evolutionary history

  • PhyML: Maximum likelihood phylogeny reconstruction

  • MrBayes: Bayesian inference of phylogeny

• Structural prediction and analysis:

  • AlphaFold2: Generate accurate structural models

  • SWISS-MODEL: Homology modeling based on crystal structures

  • PyMOL/Chimera: Visualize and compare predicted structures

• Synteny and genomic context:

  • MicrobesOnline: Analyze gene neighborhoods

  • SyntTax: Examine synteny across multiple genomes

  • IMG/M: Integrated analysis of microbial genomes

• Codon usage and tRNA analysis:

  • tRNAscan-SE: Identify tRNA genes as potential substrates

  • EMBOSS cusp: Analyze codon usage patterns

  • CodonW: Multivariate analysis of codon usage

• Comparative genomics:

  • OrthoMCL: Identify orthologs across multiple genomes

  • Roary: Pan-genome analysis of bacterial species

  • GET_HOMOLOGUES: Flexible ortholog clustering

These tools collectively provide a comprehensive framework for analyzing miaA genes, their evolution, and their genomic context across diverse bacterial species, enabling insights into adaptation and specialization.

What biosafety precautions should be implemented when working with recombinant Aliivibrio salmonicida proteins?

When working with recombinant Aliivibrio salmonicida proteins, including miaA, researchers should implement these biosafety precautions:

• Risk assessment and containment:

  • Aliivibrio salmonicida is typically handled at Biosafety Level 1 (BSL-1) as it primarily affects fish

  • Recombinant proteins derived from this organism generally pose minimal risk but require standard laboratory safety practices

• Laboratory practices:

  • Use personal protective equipment (gloves, lab coat, eye protection)

  • Implement good microbiological techniques

  • Decontaminate work surfaces before and after use

  • Properly dispose of all biological waste according to institutional guidelines

• Regulatory compliance:

  • Adhere to institutional biosafety committee guidelines

  • Ensure proper documentation of recombinant DNA work

  • Maintain records of risk assessments and safety protocols

• Special considerations:

  • Perform rigorous biosecurity and export control screening for compliance with legal and regulatory guidance

  • Consider aquaculture industry implications when working with fish pathogens

  • Implement additional precautions if expressing virulence factors

• Training requirements:

  • Ensure all personnel are trained in standard microbiological practices

  • Provide specific training on handling purified recombinant proteins

  • Document training completion and regular refresher sessions

These precautions ensure researcher safety while maintaining compliance with institutional and regulatory requirements.

How should researchers approach the potential dual-use implications of miaA research?

When considering the dual-use implications of miaA research, researchers should:

• Evaluate potential applications and risks:

  • Primary research aims: Understanding bacterial physiology and translation

  • Potential beneficial applications: Antimicrobial development, biotechnology tools

  • Possible misuse scenarios: Engineering bacterial pathogens with altered tRNA modification

• Implement responsible research practices:

  • Apply the "Do No Harm" principle to experimental design

  • Consider whether knowledge gained justifies potential risks

  • Consult institutional ethics committees for guidance

• Publication and dissemination considerations:

  • Balance scientific openness with security concerns

  • Consider whether methodological details could enable misuse

  • Follow journal guidelines for dual-use research of concern

• Regulatory compliance:

  • Adhere to national and international regulations on biological research

  • Implement appropriate biosecurity measures for sensitive materials

  • Perform export control screening as needed

• Education and awareness:

  • Train researchers in identifying dual-use implications

  • Foster a culture of responsibility within research groups

  • Engage with broader discussions on science ethics