Recombinant Dinoroseobacter shibae Methionyl-tRNA formyltransferase (fmt)

What is Methionyl-tRNA formyltransferase (fmt) and what reaction does it catalyze?

Methionyl-tRNA formyltransferase (EC 2.1.2.9) is an enzyme that catalyzes the transfer of a formyl group from 10-formyltetrahydrofolate to methionyl-tRNA, producing N-formylmethionyl-tRNA and tetrahydrofolate as products . The systematic name for this enzyme is 10-formyltetrahydrofolate:L-methionyl-tRNA N-formyltransferase. The reaction can be represented as:

10-formyltetrahydrofolate + L-methionyl-tRNA(fMet) + H₂O → tetrahydrofolate + N-formylmethionyl-tRNA(fMet)

This enzyme belongs to the family of transferases that transfer one-carbon groups, specifically the hydroxymethyl-, formyl- and related transferases . In bacterial systems, this reaction is essential for initiating protein synthesis, as N-formylmethionyl-tRNA serves as the initiator tRNA during translation.

What metabolic pathways involve fmt in Dinoroseobacter shibae?

Methionyl-tRNA formyltransferase participates in three key metabolic pathways in D. shibae:

• Methionine metabolism - involving the processing of methionyl-tRNA for protein synthesis initiation

• One carbon pool by folate - utilizing 10-formyltetrahydrofolate as a one-carbon donor

• Aminoacyl-tRNA biosynthesis - essential for the production of charged tRNAs for translation

These pathways are interconnected and crucial for cellular function in D. shibae, which is a Gram-negative photoheterotrophic bacterium that performs aerobic anoxygenic photosynthesis .

What are the optimal storage and handling conditions for recombinant D. shibae fmt?

For optimal stability and activity, recombinant D. shibae fmt should be stored according to the following guidelines:

Repeated freezing and thawing should be avoided to maintain protein integrity . For reconstitution:

• Centrifuge the vial briefly before opening to bring contents to the bottom

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

• Add 5-50% glycerol (final concentration) for long-term storage

• The default recommended final concentration of glycerol is 50%

These conditions ensure optimal enzyme stability for experimental applications.

How can researchers verify the purity and activity of recombinant D. shibae fmt?

Researchers should employ multiple analytical techniques to verify purity and activity:

• Purity verification:

  • SDS-PAGE analysis (expect >85% purity as indicated in product specifications)

  • Western blotting using anti-fmt or anti-tag antibodies (depending on the tag used during expression)

  • Mass spectrometry to confirm protein identity and detect potential contaminants

• Activity assessment:

  • Enzymatic assay measuring the transfer of formyl groups from 10-formyltetrahydrofolate to methionyl-tRNA

  • Monitoring the formation of N-formylmethionyl-tRNA using HPLC or similar chromatographic techniques

  • Radioactive assays using labeled substrates to quantify reaction kinetics

The specific tag information should be verified during the manufacturing process, as this can affect both purification strategies and potential activity measurements .

How does fmt function relate to D. shibae's adaptation to oxidative stress?

D. shibae inhabits the photic zone of marine ecosystems where it is frequently exposed to oxygen that forms highly reactive species . While no direct evidence links fmt specifically to oxidative stress response in the provided materials, several connections can be hypothesized based on the data:

• Protein synthesis regulation is a critical aspect of stress response, and fmt's role in translation initiation could potentially be modulated during oxidative stress.

• Comprehensive proteomic analysis of D. shibae identified 2580 proteins, with 75 proteins changing significantly in response to peroxide stress, 220 to superoxide stress, and 207 to thiol stress . Further research would be needed to determine if fmt is among these proteins.

• D. shibae employs multiple stress response mechanisms, including thioredoxin and peroxiredoxin systems , which could potentially interface with fmt-mediated processes.

A targeted study examining fmt expression and activity under various oxidative stress conditions would help elucidate its potential role in stress adaptation.

What is the relationship between fmt and the unique metabolic capabilities of D. shibae?

D. shibae possesses several distinctive metabolic capabilities that may intersect with fmt function:

• Aerobic anoxygenic photosynthesis: Unlike closely related phototrophic purple bacteria, D. shibae performs aerobic anoxygenic photosynthesis, requiring organic substrates like succinate, glucose, and glycerol as carbon and energy sources . Fmt-mediated protein synthesis regulation might be critical for expressing the photosynthetic apparatus under appropriate conditions.

• Adaptation to anaerobic conditions: Transposon mutagenesis has identified chromosomal and plasmid genes essential for adaptation to anaerobic conditions . While fmt was not specifically mentioned among these genes, its role in initiating translation could be important for expressing proteins needed during aerobic-anaerobic transitions.

• Outer membrane vesicle (OMV) formation: D. shibae secretes DNA-containing OMVs constitutively during growth . The proteins involved in this process require proper synthesis, potentially involving fmt-initiated translation.

Future research comparing fmt activity and expression under different metabolic states could reveal its specific contributions to D. shibae's unique physiological capabilities.

How can site-directed mutagenesis be applied to study critical residues in D. shibae fmt?

Site-directed mutagenesis represents a powerful approach for investigating structure-function relationships in D. shibae fmt. Based on the protein sequence provided , researchers can target specific residues predicted to be involved in:

• Substrate binding: Identify residues likely involved in binding 10-formyltetrahydrofolate and methionyl-tRNA through sequence alignment with structurally characterized fmt enzymes (e.g., those with PDB codes 1FMT and 2FMT ).

• Catalytic activity: Target residues in motifs conserved across formyltransferases that may participate directly in catalysis.

• Protein stability: Modify residues that contribute to secondary structure elements or hydrophobic cores.

Methodological approach:

• Generate a collection of single-residue mutants using PCR-based mutagenesis

• Express and purify mutant proteins using the same E. coli system as for wild-type protein

• Characterize mutants through activity assays, thermal stability measurements, and structural analyses

• Correlate findings with the three metabolic pathways involving fmt

This systematic approach would yield insights into critical functional domains and potentially reveal unique features of the D. shibae enzyme compared to homologs from other species.

How might fmt function intersect with D. shibae's outer membrane vesicle (OMV) production?

D. shibae secretes DNA-containing OMVs constitutively during growth, with time-lapse microscopy capturing instances of multiple OMV production at the septum of dividing cells . While no direct connection between fmt and OMV production is established in the provided materials, potential intersections merit investigation:

• Protein synthesis for OMV components: The OMV proteome is dominated by outer membrane and periplasmic proteins, particularly those predicted to interact with peptidoglycan during cell division (LysM, Tol-Pal, Spol, and lytic murein transglycosylase) . Fmt-mediated translation initiation could be critical for the proper expression of these proteins.

• Regulation during cell division: OMV production appears coupled to cell division , a process requiring tightly coordinated protein synthesis, which depends on fmt activity for initiation.

• Response to stress conditions: Both OMV production and fmt activity might be modulated under stress conditions, such as oxidative stress, which D. shibae regularly encounters in its marine habitat .

Experimental approaches to investigate these connections could include:

• Comparing fmt expression and activity during peak OMV production phases

• Examining the effects of fmt inhibition on OMV composition and production

• Analyzing whether fmt itself or its products are present in OMVs

What techniques are most effective for measuring fmt activity in cell-free extracts of D. shibae?

Assessing fmt activity in cell-free extracts requires sensitive and specific techniques to capture the formylation of methionyl-tRNA. Based on the enzymatic properties of fmt, several approaches are recommended:

• Radioisotope-based assays:

  • Use ³H-labeled or ¹⁴C-labeled 10-formyltetrahydrofolate as substrate

  • Measure the transfer of labeled formyl groups to methionyl-tRNA

  • Quantify via scintillation counting after isolating the formylated tRNA

• HPLC-based methods:

  • Separate and quantify the reaction products (N-formylmethionyl-tRNA and tetrahydrofolate)

  • Monitor changes in substrate (methionyl-tRNA and 10-formyltetrahydrofolate) concentrations

  • Compare results to standard curves for accurate quantification

• Mass spectrometry:

  • Use LC-MS/MS to identify and measure formylated versus non-formylated methionyl-tRNA

  • This approach offers high sensitivity and specificity for product detection

• Coupled enzyme assays:

  • Design assays that link fmt activity to the production of a spectrophotometrically detectable product

  • Monitor reaction progress in real-time

Optimization considerations for D. shibae extracts:

• Buffer composition should mimic the marine environment where D. shibae naturally occurs

• Include appropriate salt concentrations to maintain native protein conformation

• Consider the effects of oxidative conditions, given D. shibae's exposure to oxygen in its natural habitat

How does fmt activity in D. shibae compare with the enzyme from other marine bacteria?

Comparative analysis of fmt across marine bacterial species can provide insights into evolutionary adaptations and functional specialization. While the search results don't directly compare D. shibae fmt to other species, a framework for such comparisons would include:

D. shibae's adaptation to its specific ecological niche in the photic zone of marine ecosystems may have driven unique evolutionary adaptations in its fmt enzyme. The enzyme's potential involvement in responding to oxidative stress and the bacterium's distinctive capability for aerobic anoxygenic photosynthesis suggest that comparative studies might reveal specialized features of D. shibae fmt compared to homologs from other marine bacteria.

How might fmt be involved in D. shibae's adaptation to anaerobic conditions?

Transposon mutagenesis has identified numerous chromosomal and plasmid genes essential for adaptation of D. shibae to anaerobic conditions . While fmt was not specifically mentioned among these genes, several connections warrant investigation:

• Metabolic reprogramming: The transition to anaerobic conditions requires significant changes in protein expression patterns. As fmt initiates protein synthesis, its activity could be regulated during this transition to facilitate the expression of proteins needed for anaerobic metabolism.

• Stress response pathways: Anaerobic adaptation involves stress response mechanisms that may intersect with fmt-mediated processes. For example, mutations in genes involved in dissimilatory and assimilatory nitrate reduction (napA, nasA) and corresponding cofactor biosynthesis (moaB, moeB, dsbC, dsbD, ccmH) cause anaerobic growth defects .

• Plasmid-encoded functions: The essential contribution of plasmid genes to anaerobic growth was confirmed with plasmid-cured D. shibae strains . If fmt has plasmid-encoded regulators or interacting partners, this could represent another connection point.

Future research could explore fmt expression and activity under aerobic versus anaerobic conditions, potentially revealing regulatory mechanisms that adjust translation initiation during metabolic shifts.

What methodological approaches can overcome challenges in studying fmt in marine bacteria?

Studying fmt in marine bacteria like D. shibae presents several unique challenges that require specialized methodological approaches:

• Cultivation challenges:

  • Implement artificial seawater medium as used in D. shibae studies

  • Maintain appropriate light conditions if studying interactions with photosynthetic processes

  • Consider the role of succinate as a carbon source, which D. shibae uses in the dark

• Genetic manipulation strategies:

  • Utilize transposon mutagenesis approaches similar to those that successfully identified genes essential for anaerobic adaptation

  • Develop targeted gene knockout and complementation systems specific to D. shibae

  • Consider the implications of D. shibae's multiple plasmids when designing genetic experiments

• Protein analysis techniques:

  • Employ the GeLC-MS/MS approach successfully used for proteomic analysis of D. shibae under oxidative stress

  • Adapt reconstitution procedures to account for the marine environment's ionic strength

  • Consider the potential effects of oxidative conditions on protein stability and activity

• Functional assays:

  • Design assays that can detect fmt activity under varying oxygen tensions

  • Account for potential interactions with marine-specific metabolites

  • Consider the temporal dynamics of D. shibae's growth and metabolic cycles

These methodological considerations would enhance the relevance and reproducibility of fmt studies in D. shibae and potentially other marine bacteria.