Recombinant Mycoplasma pneumoniae Probable 5-formyltetrahydrofolate cyclo-ligase (MPN_348)

What is MPN_348 and what is its function in Mycoplasma pneumoniae?

MPN_348 is the gene encoding the probable 5-formyltetrahydrofolate cyclo-ligase in Mycoplasma pneumoniae strain 29342/M129. This enzyme plays a crucial role in folate metabolism by catalyzing the ATP-dependent conversion of 5-formyltetrahydrofolate (folinic acid) to 5,10-methenyltetrahydrofolate. In Mycoplasma pneumoniae, which has a minimal genome, this enzyme is particularly important for maintaining one-carbon metabolism necessary for nucleotide synthesis and amino acid metabolism. The enzyme helps recycle 5-formyltetrahydrofolate, which is a stable storage form of folate but not directly used in one-carbon transfer reactions, back into the metabolically active folate pool .

This function is especially critical in M. pneumoniae due to its reduced genome with limited metabolic redundancy. The bacterium, known as the causative agent of atypical pneumonia, must efficiently manage its folate resources to maintain essential cellular processes while successfully establishing infection in the host environment.

What is the enzymatic reaction catalyzed by 5-formyltetrahydrofolate cyclo-ligase?

The enzymatic reaction catalyzed by 5-formyltetrahydrofolate cyclo-ligase (EC 6.3.3.2) is:

ATP + 5-formyltetrahydrofolate → ADP + phosphate + 5,10-methenyltetrahydrofolate

This reaction involves the ATP-dependent formation of an intramolecular carbon-nitrogen bond, creating a cyclic structure in the folate molecule. The enzyme uses ATP to activate the formyl group of 5-formyltetrahydrofolate, facilitating the nucleophilic attack by the N10 nitrogen and resulting in the formation of 5,10-methenyltetrahydrofolate . The reaction requires magnesium ions as a cofactor, which help coordinate the ATP molecule and stabilize the developing negative charges during catalysis .

The structure of 5-formyltetrahydrofolate cyclo-ligase from Bacillus anthracis, determined by X-ray crystallography at 1.6 Å resolution, provides valuable insights into this reaction mechanism. The structure, solved in complex with magnesium-ion-bound ADP and phosphate, reveals the precise spatial arrangement of catalytic residues that create the optimal environment for this conversion .

How is MPN_348 classified within enzyme families?

MPN_348 encodes a 5-formyltetrahydrofolate cyclo-ligase (EC 6.3.3.2) which belongs to the family of ligases, specifically the cyclo-ligases that form carbon-nitrogen bonds. The systematic name for this enzyme class is 5-formyltetrahydrofolate cyclo-ligase (ADP-forming). It is also known by several other names including 5,10-methenyltetrahydrofolate synthetase (MTHFS), formyltetrahydrofolic cyclodehydrase, and 5-formyltetrahydrofolate cyclodehydrase .

Structurally, 5-formyltetrahydrofolate cyclo-ligase belongs to the NagB/RpiA/CoA transferase-like superfamily of enzymes, which share a common structural fold and the ability to bind phosphate-containing molecules . This classification is based on the three-dimensional structure of the protein, which consists of a central layer of mixed (parallel and antiparallel) β-sheet flanked by helices on either side, forming an α+β fold . The members of this superfamily are involved in a diverse range of metabolic processes but share the common property of phosphate binding, which is essential for the ATP-dependent activity of MPN_348.

What is known about the structure of 5-formyltetrahydrofolate cyclo-ligase?

While the specific structure of MPN_348 from Mycoplasma pneumoniae has not been determined at high resolution based on the provided search results, structural information is available for homologous 5-formyltetrahydrofolate cyclo-ligase enzymes from other species, notably Bacillus anthracis. The B. anthracis enzyme structure was determined by X-ray crystallography at a resolution of 1.6 Å, in complex with magnesium-ion-bound ADP and phosphate .

The enzyme forms a single domain with an α+β fold, consisting of a central layer of mixed (parallel and antiparallel) β-sheet flanked by helices on either side. This fold belongs to the NagB/RpiA/CoA transferase-like superfamily of enzymes . The active site contains a bound magnesium ion coordinated with ADP and phosphate, providing insights into the catalytic mechanism of the enzyme.

The MPN_348 protein from Mycoplasma pneumoniae strain 29342/M129 is 164 amino acids in length with a molecular weight of approximately 19,265 Da . The protein sequence (MDKNALRKQILQKRMALSTIEKSHLDQKINQKLVAFLTPKPCIKTIALYEPIKNEVTFVDFFFEFLKINQIRAVYPKVISDTEIIFIDQETNTFEPNQIDCFLIPLVGFNKDNYRLGFKGYYDRYLMQLTRQQPKIGIAYSFQKGDFLADPWDVQLDIINDE) likely adopts a similar fold to the B. anthracis enzyme given the conserved catalytic function .

How does ATP binding affect the structure and function of MPN_348?

ATP binding plays a crucial role in the structure and function of 5-formyltetrahydrofolate cyclo-ligase enzymes like MPN_348. Based on structural studies of homologous enzymes, the following ATP-dependent effects are observed:

• Conformational changes: ATP binding induces significant conformational changes in the enzyme structure, transitioning from an "open" to a "closed" state. This conformational change helps position the substrates correctly for catalysis and excludes water from the active site, preventing unproductive hydrolysis of ATP .

• Magnesium coordination: ATP typically binds in complex with magnesium ions, which coordinate the phosphate groups of ATP and critical active site residues. This coordination is essential for proper positioning of ATP and for neutralizing the negative charges on the phosphate groups .

• Activation of the reaction: The γ-phosphate of ATP serves as a leaving group in the reaction, and its binding orients the molecule for optimal interaction with the formyl group of 5-formyltetrahydrofolate. This positioning is critical for the subsequent formation of the carbon-nitrogen bond .

• Transition state stabilization: The binding energy derived from ATP interaction with the enzyme contributes to lowering the activation energy of the reaction by stabilizing the transition state during catalysis.

The detailed structural analysis of the B. anthracis enzyme with bound ADP and phosphate provides insights into the post-reaction state, revealing how the products are coordinated in the active site . The spatial arrangement of these components illustrates the precise molecular interactions that drive the enzymatic conversion, which are likely conserved in the MPN_348 enzyme given the fundamental nature of this catalytic mechanism.

What expression systems are optimal for producing recombinant MPN_348?

Based on the information in the search results, recombinant MPN_348 protein can be expressed in several systems, each with advantages and limitations:

• E. coli expression system:

  • Advantages: Rapid growth, high yield, well-established protocols, cost-effective

  • Limitations: Potential issues with protein folding, lack of post-translational modifications

  • Optimization strategies: Use of specialized strains (e.g., BL21(DE3), Rosetta), low-temperature induction

• Yeast expression system:

  • Advantages: Eukaryotic processing capabilities, proper folding of complex proteins

  • Limitations: Longer expression time, hypermannosylation can occur

  • Recommended for: Cases where E. coli expression yields inactive protein

• Baculovirus expression system:

  • Advantages: Higher eukaryotic system, efficient folding, suitable for large or complex proteins

  • Limitations: More time-consuming, technically demanding, higher cost

  • Particularly useful for: Proteins requiring complex folding

• Mammalian cell expression system:

  • Advantages: Most authentic post-translational modifications, proper folding

  • Limitations: Lower yields, highest cost, slowest expression time

  • Reserved for: Cases where proper folding absolutely requires mammalian cellular machinery

For MPN_348, E. coli expression is often the first choice due to its simplicity and cost-effectiveness. The protein has been successfully expressed with N-terminal and potentially C-terminal tags . The specific choice of expression system should be guided by the requirements of the intended experiments, with considerations for protein yield, purity, activity, and authenticity.

What purification strategies yield the highest purity and activity for MPN_348?

Effective purification of recombinant MPN_348 typically involves a multi-step process designed to achieve high purity while maintaining enzymatic activity:

• Initial capture step:

  • Affinity chromatography: Utilizing the N-terminal or C-terminal tags commonly added to recombinant MPN_348

  • For His-tagged protein: Immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins

  • Typical conditions: Binding in buffer containing 20-50 mM imidazole to reduce non-specific binding, elution with 250-500 mM imidazole

• Intermediate purification:

  • Ion exchange chromatography: Based on the theoretical pI of MPN_348

  • Size exclusion chromatography: To separate monomeric protein from aggregates and to perform buffer exchange

• Polishing step:

  • Hydroxyapatite chromatography or hydrophobic interaction chromatography

  • Second round of size exclusion in final storage buffer

Critical factors affecting purification outcomes include buffer composition (pH, salt concentration, and addition of stabilizing agents), temperature (maintaining low temperature throughout purification), protease inhibitors (during initial lysis), and reducing agents (to prevent oxidation of cysteine residues) .

The final purified product should be analyzed by SDS-PAGE to confirm purity (≥85% as mentioned in the search results) and by activity assays to ensure that the enzyme remains functional after purification . Small volumes of MPN_348 recombinant protein vial(s) may occasionally become entrapped in the seal of the product vial during shipment and storage, requiring brief centrifugation before use .

How can protein stability be maintained during storage and experimental procedures?

Maintaining the stability of recombinant MPN_348 during storage and experimental procedures is crucial for preserving enzymatic activity. Based on general protein handling principles and specific information from the search results:

Storage conditions:

• Temperature options:

  • Long-term storage: -80°C is optimal for extended periods

  • Medium-term storage: -20°C is suitable for several months

  • Working aliquots: 4°C for up to one week

• Formulation considerations:

  • Buffer composition: Typically 20-50 mM Tris or phosphate buffer, pH 7.0-8.0

  • Salt content: 100-150 mM NaCl to maintain protein solubility

  • Glycerol addition: 10-20% glycerol acts as a cryoprotectant for frozen storage

  • Reducing agents: 1-5 mM DTT or β-mercaptoethanol to prevent oxidation

  • Stabilizing additives: Consider specific cofactors like magnesium ions

• Physical state:

  • Lyophilized form: Provides maximum stability for long-term storage

  • Liquid form: More convenient for immediate use but less stable long-term

Handling recommendations:

• Avoid repeated freeze-thaw cycles: Prepare small single-use aliquots before freezing

• Centrifuge before use: Briefly centrifuge protein vials that may have liquid entrapped in the seal

• Temperature transitions: Allow frozen protein to thaw completely at 4°C before use

• Concentration considerations: Maintain protein at optimal concentration to prevent aggregation

By carefully controlling these factors, the stability and activity of recombinant MPN_348 can be maintained throughout storage and experimental procedures, ensuring reliable and reproducible research outcomes.

What assays are available to measure MPN_348 enzymatic activity?

Several complementary assays can be employed to measure the enzymatic activity of 5-formyltetrahydrofolate cyclo-ligase (MPN_348), each with specific advantages and limitations:

• Spectrophotometric assays:

  • Based on the differential absorption spectra of substrate and product

  • 5,10-methenyltetrahydrofolate exhibits strong absorbance at 355 nm (ε = 25,100 M⁻¹cm⁻¹) at acidic pH

  • Reaction can be monitored by measuring the increase in absorbance at 355 nm in real-time

  • Advantages: Continuous, rapid, amenable to high-throughput screening

  • Limitations: Potential interference from other compounds absorbing in the UV range

• HPLC-based assays:

  • Separation of substrate and product based on their distinct retention times

  • Detection by UV absorbance or fluorescence

  • Advantages: Highly specific, quantitative, can detect multiple folate species simultaneously

  • Limitations: Lower throughput, more time-consuming, requires specialized equipment

• Coupled enzyme assays:

  • Linking the formation of ADP to the oxidation of NADH through pyruvate kinase and lactate dehydrogenase

  • Monitors decrease in NADH absorbance at 340 nm

  • Advantages: Continuous, can be performed in multi-well format

  • Limitations: Indirect measurement, potential interference from coupling enzymes

Standard reaction conditions typically include:

Control reactions should include omission of each substrate and enzyme to confirm the specificity of the assay and establish background rates.

How can MPN_348 be used as a target for antimicrobial development against Mycoplasma pneumoniae?

MPN_348 (5-formyltetrahydrofolate cyclo-ligase) represents a potential target for antimicrobial development against Mycoplasma pneumoniae due to its critical role in folate metabolism. Strategic approaches to targeting this enzyme include:

• Structural basis for selective inhibition:

  • Comparison of bacterial (MPN_348) and human 5-formyltetrahydrofolate cyclo-ligase structures

  • Identification of structural differences in the active site or substrate binding regions

  • Rational design of inhibitors that selectively bind to bacterial enzyme over human homolog

  • Crystal structures with bound ADP and phosphate provide valuable information about the active site architecture

• High-throughput screening approaches:

  • Development of enzyme-based assays suitable for screening compound libraries

  • Primary screening using spectrophotometric assays monitoring 5,10-methenyltetrahydrofolate formation

  • Secondary screening of hits using more specific assays and counter-screening against human enzyme

• Inhibitor design strategies:

  • ATP-competitive inhibitors: Compounds that compete with ATP binding

  • Folate-competitive inhibitors: Analogues of 5-formyltetrahydrofolate

  • Bisubstrate inhibitors: Linking features of both substrates

  • Allosteric inhibitors: Targeting sites distant from the active site that affect enzyme function

• Integration with antimicrobial susceptibility data:

  • Consideration of existing antimicrobial resistance patterns in M. pneumoniae

  • Combination approaches with established antibiotics

  • Development of inhibitors active against macrolide-resistant strains

The development pathway would involve iterative cycles of compound design, synthesis, and testing, guided by structural information and mechanistic understanding of the enzyme. Given the emerging resistance of M. pneumoniae to established antibiotics like macrolides, as highlighted in research on antimicrobial susceptibilities among M. pneumoniae isolates, novel targets like MPN_348 represent important opportunities for developing new antimicrobial agents .

How can site-directed mutagenesis be used to study MPN_348 function?

Site-directed mutagenesis represents a powerful approach to investigate the structure-function relationships of MPN_348. This technique allows researchers to make precise changes to specific amino acid residues and observe the resulting effects on enzyme activity, stability, and substrate binding. The systematic application of site-directed mutagenesis to MPN_348 can provide valuable insights through the following strategies:

• Catalytic residue identification and validation:

  • Mutation of predicted active site residues involved in ATP binding

  • Alteration of residues coordinating the essential magnesium ion

  • Mutation of residues predicted to interact with the 5-formyltetrahydrofolate substrate

  • Conservative (similar amino acid) and non-conservative (different property) mutations to assess the specific requirements at each position

• Experimental approach:

  • Design of mutagenic primers incorporating desired nucleotide changes

  • PCR-based mutagenesis using methods like QuikChange or overlap extension PCR

  • Verification of mutations by DNA sequencing

  • Expression and purification of mutant proteins using identical conditions to wild-type

  • Comparative analysis of enzyme activity, substrate affinity, and structural stability

• Structural element analysis:

  • Mutation of residues in flexible loops near the active site

  • Introduction or removal of disulfide bonds to assess structural rigidity effects

  • Truncation analysis to identify essential domains or regions

  • Interface residue mutations if MPN_348 functions as a dimer or multimer

• Analytical techniques for mutant characterization:

The results from systematic mutagenesis can be mapped onto the structural model of MPN_348 (or a homology model based on related structures like the B. anthracis enzyme) to create a comprehensive picture of structure-function relationships . This information is valuable not only for fundamental understanding of enzyme mechanism but also for rational design of inhibitors targeting specific features of the bacterial enzyme.

How does MPN_348 contribute to Mycoplasma pneumoniae pathogenicity?

Understanding the relationship between MPN_348 (5-formyltetrahydrofolate cyclo-ligase) and M. pneumoniae pathogenicity requires investigation at multiple levels, from basic metabolism to host-pathogen interactions:

• Metabolic contributions to pathogenicity:

  • Folate metabolism is essential for nucleotide synthesis and methylation reactions

  • MPN_348 helps maintain the active folate pool by recycling 5-formyltetrahydrofolate

  • Mycoplasma pneumoniae has a reduced genome with limited metabolic redundancy, potentially making folate metabolism enzymes critical for survival during infection

  • Connection between folate metabolism and bacterial replication rates during infection

• Experimental approaches to assess essentiality:

  • Conditional knockdown or depletion systems to reduce MPN_348 expression

  • CRISPR interference (CRISPRi) approaches adapted for Mycoplasma

  • Genetic complementation studies

  • Specific chemical inhibition coupled with growth and virulence assessment

• Host-pathogen interaction considerations:

  • Competition for folate between host and pathogen

  • Effect of host folate levels on bacterial growth and MPN_348 expression

  • Potential modulation of host immune responses through folate-dependent pathways

  • Investigation of MPN_348 expression during different phases of infection

• Connection to antimicrobial resistance:

  • Relationship between folate metabolism and resistance to commonly used antibiotics

  • Potential compensatory role of enhanced folate metabolism in resistant strains

  • Consideration of the antimicrobial resistance patterns observed in clinical isolates

  • Development of combination therapies targeting multiple metabolic pathways

This multi-faceted approach would provide a comprehensive understanding of how MPN_348 contributes to the pathogenicity of Mycoplasma pneumoniae and potentially identify new strategies for therapeutic intervention, particularly important in light of increasing antimicrobial resistance in M. pneumoniae infections .

What structural differences between MPN_348 and human 5-formyltetrahydrofolate cyclo-ligase can be exploited for drug design?

Exploiting structural differences between bacterial MPN_348 and the human homolog of 5-formyltetrahydrofolate cyclo-ligase presents an opportunity for selective inhibitor design. A systematic approach to identifying and leveraging these differences would include:

• Comparative structural analysis:

  • Superposition of bacterial and human enzyme structures (or homology models)

  • Identification of differences in active site architecture and substrate binding pockets

  • Analysis of surface charge distribution and solvent accessibility

  • Evaluation of protein dynamics and conformational flexibility differences

• Active site differences to exploit:

  • Sequence variation in residues directly contacting substrates

  • Differences in the ATP binding pocket geometry

  • Variations in the folate binding region

  • Unique structural features that could accommodate selective inhibitors

• Structure-based design strategies:

  • Fragment-based approaches targeting unique pockets

  • Structure-activity relationship studies guided by comparative models

  • Molecular dynamics simulations to identify transient pockets

  • Virtual screening focused on species-specific features

The structural information available for the B. anthracis enzyme in complex with magnesium-ion-bound ADP and phosphate provides valuable insights that can be extrapolated to MPN_348 . This structure reveals detailed interactions in the active site that might differ from the human enzyme, potentially allowing for the design of inhibitors that selectively target the bacterial enzyme while sparing the human homolog.

The goal of such selective inhibition would be particularly important for addressing the growing concern of macrolide-resistant Mycoplasma pneumoniae (MRMP) infections that have become increasingly prevalent, especially in East Asia, as documented in recent antimicrobial susceptibility studies .

How does antimicrobial resistance in Mycoplasma pneumoniae affect MPN_348 function?

Investigating the relationship between antimicrobial resistance in Mycoplasma pneumoniae and MPN_348 function requires consideration of both direct and indirect effects:

• Direct effects of resistance mechanisms on MPN_348:

  • Assessment of whether mutations conferring antimicrobial resistance occur in or near the MPN_348 gene

  • Evaluation of potential horizontal gene transfer affecting MPN_348 sequence or expression

  • Investigation of whether resistance-associated mutations in other genes indirectly affect MPN_348 function

• Comparative analysis of resistant vs. susceptible strains:

  • Transcriptomic analysis to compare MPN_348 expression levels

  • Proteomic studies to evaluate MPN_348 protein abundance

  • Sequencing of MPN_348 gene in clinical isolates with different resistance profiles

  • Functional characterization of MPN_348 enzyme from resistant and susceptible strains

• Metabolic adaptations in resistant strains:

  • Changes in folate metabolism pathways in response to antimicrobial pressure

  • Compensatory metabolic adaptations that might affect MPN_348 substrate availability

  • Integration with information about antimicrobial susceptibility patterns observed in M. pneumoniae isolates

Understanding these relationships is particularly relevant in light of the increasing prevalence of macrolide-resistant Mycoplasma pneumoniae (MRMP) infections. Recent studies have shown that macrolide-resistant M. pneumoniae strains have point mutations that are implicated in conferring resistance, and monitoring the antibiotic susceptibility of M. pneumoniae and identifying mutations in the resistant strains is crucial for effective disease management .

The observation that resistance to macrolides does not necessarily confer resistance to other antimicrobial classes suggests that novel targets like MPN_348 might be effective against resistant strains. Studies have shown that while macrolide resistance is common, none of the strains tested were resistant to fluoroquinolones or tetracyclines, indicating that alternative metabolic pathways might be targeted in resistant strains .