Recombinant Methylacidiphilum infernorum Undecaprenyl-diphosphatase (uppP)

What is Methylacidiphilum infernorum and why is it significant for research?

Methylacidiphilum infernorum strain V4 is an extremely acidophilic methanotroph belonging to the bacterial phylum Verrucomicrobia. Unlike proteobacterial methanotrophs, M. infernorum has a distinctive metabolic profile where it fixes carbon autotrophically and uses methane exclusively for energy generation rather than as a carbon source . This unique metabolic characteristic makes it a significant organism for studying alternative methanotrophic pathways. The bacterium represents an important model for investigating microbial adaptation to extreme environmental conditions, particularly acidic, high-temperature geothermal environments. Research on M. infernorum has expanded our understanding of microbial diversity and metabolic versatility, revealing non-proteobacterial methanotrophy that might have been overlooked in previous environmental studies .

What is Undecaprenyl-diphosphatase (uppP) and what role does it play in bacterial physiology?

Undecaprenyl-diphosphatase (uppP), also known as Bacitracin resistance protein or Undecaprenyl pyrophosphate phosphatase (EC 3.6.1.27), is a crucial enzyme involved in bacterial cell wall biosynthesis . The enzyme functions in the peptidoglycan synthesis pathway by recycling the lipid carrier undecaprenyl phosphate. Specifically, uppP dephosphorylates undecaprenyl diphosphate to generate undecaprenyl phosphate, which is essential for the transport of peptidoglycan precursors across the cytoplasmic membrane. This process is critical for cell wall assembly and bacterial survival. In the context of antibiotic resistance, uppP contributes to bacitracin resistance by maintaining the pool of available undecaprenyl phosphate carriers, allowing bacteria to continue cell wall synthesis despite the presence of antibiotics that target this pathway .

How does the structure of M. infernorum uppP compare to other bacterial undecaprenyl-diphosphatases?

M. infernorum uppP is a membrane protein consisting of 268 amino acids with a sequence that suggests multiple transmembrane helices . The protein contains characteristic hydrophobic regions consistent with its membrane-embedded nature and function. The amino acid sequence (MHDLWPTILLGIIEGLSEFLPISSTGHLLVAEHWLGERSETFNIFIQLGAVLAVCLIYKE RLSSFLFLWKDREKLPYFLKLSVAFIITSILGLWVKKMGWELPKDLGPVIIAIFGGAFWI YFTEKVSSQRQSFVEEISWPTAIAVGASQVVAGVLPGFSRSAATILMAVLLGVSRPAATE FAFLLGIPTMFAASLFAWIEETHFLKNPSLDSPLTLATGFCVS) reveals conserved motifs typical of membrane phosphatases .

While structurally similar to other bacterial undecaprenyl-diphosphatases, M. infernorum uppP likely possesses unique adaptations reflecting the extremophilic nature of its source organism. These adaptations may include modifications that enhance protein stability under acidic conditions and high temperatures characteristic of the geothermal environments where M. infernorum thrives .

What are the optimal conditions for expressing recombinant M. infernorum uppP?

The expression of recombinant M. infernorum uppP requires careful optimization due to its membrane protein nature. Based on established protocols for similar enzymes, the following conditions are recommended:

Expression System Selection:

• E. coli expression systems with specialized strains (C41(DE3), C43(DE3), or Lemo21(DE3)) designed for membrane protein expression are preferred

• Alternative systems such as yeast (P. pastoris) may be considered for difficult-to-express constructs

Expression Conditions:

• Induction with lower IPTG concentrations (0.1-0.5 mM) to prevent formation of inclusion bodies

• Lower growth temperatures (16-25°C) during induction to enhance proper folding

• Extended expression times (16-24 hours) for maximum yield of functional protein

• Addition of membrane-stabilizing agents such as glycerol (5-10%) to the growth medium

For purification and storage, protocols similar to those used for the commercially available recombinant protein should be followed, utilizing Tris-based buffers with 50% glycerol for stabilization . The enzyme should be stored at -20°C for short-term use or -80°C for extended storage, with working aliquots maintained at 4°C for up to one week to avoid repeated freeze-thaw cycles that could compromise enzyme activity .

How can enzymatic activity of recombinant uppP be accurately measured?

The enzymatic activity of recombinant M. infernorum uppP can be measured using several complementary approaches:

Continuous Spectrophotometric Assay:
Similar to the assay described for UPPS, a continuous spectrophotometric assay can be adapted for uppP by monitoring the release of inorganic phosphate from undecaprenyl diphosphate . The assay typically includes:

• A chromogenic phosphate detection system (e.g., using MESG, malachite green, or EnzChek phosphate assay)

• Appropriate buffer system (typically pH 5.5-7.5 to accommodate the acidophilic nature of the enzyme)

• Detergent (0.01% v/v Triton X-100) to solubilize the lipid substrate

• Divalent cations (Mg²⁺ or Mn²⁺) as cofactors

• Temperature control (37-55°C depending on experimental objectives)

Radiometric Assay:
For greater sensitivity, a radiometric assay using ³²P-labeled substrates can be employed . This approach allows direct quantification of dephosphorylation activity through detection of released radioactive phosphate.

Data Analysis:
Results should be analyzed using appropriate enzyme kinetics models, with IC₅₀ values for inhibitors determined by fitting inhibition data to dose-response curves using software such as GraphPad PRISM .

What approaches can be used to study the interaction between uppP and potential inhibitors?

Studying interactions between M. infernorum uppP and potential inhibitors requires a multi-faceted approach:

In Vitro Enzyme Inhibition Assays:

• Perform dose-dependent inhibition studies using purified recombinant uppP

• Determine IC₅₀ values through enzyme activity measurements as described above

• Establish inhibition mechanisms (competitive, non-competitive, uncompetitive) through kinetic analysis

Binding Affinity Measurements:

• Isothermal titration calorimetry (ITC) to measure binding thermodynamics

• Surface plasmon resonance (SPR) for real-time binding kinetics

• Microscale thermophoresis (MST) for interactions in solution

Structural Studies:

• X-ray crystallography of enzyme-inhibitor complexes

• NMR studies for dynamic interaction analysis

• In silico molecular docking and MD simulations using homology models if crystal structures are unavailable

Validation in Biological Systems:

• Growth inhibition assays against model organisms

• Synergy studies with established antibiotics using checkerboard assays and calculating fractional inhibitory concentration indices (FICI)

• Evaluation of resistance development through passage experiments

This multi-level approach provides comprehensive characterization of inhibitor interactions, from molecular binding to biological effects, essential for understanding structure-activity relationships.

How can M. infernorum uppP contribute to antibiotic development research?

M. infernorum uppP represents a valuable target for antibiotic development research for several reasons:

Synergistic Approach to Combat Resistance:
Inhibitors targeting enzymes in the peptidoglycan biosynthesis pathway have shown potential to restore sensitivity to existing antibiotics in resistant bacteria. For example, compounds that inhibit UPPS (which functions in the same pathway as uppP) have demonstrated synergism with methicillin against MRSA (FICI value of 0.11, indicating strong synergism) . Similar synergistic effects might be achieved with uppP inhibitors.

Exploitation of Structural Differences:
The structural and functional characterization of M. infernorum uppP may reveal unique features that can be exploited for selective inhibition. This could lead to antibiotics with improved specificity for certain bacterial pathogens while minimizing effects on beneficial microbiota.

Experimental Framework:
Research approaches should include:

• Structure-based inhibitor design guided by uppP structural data

• High-throughput screening of compound libraries against purified uppP

• Lead optimization through medicinal chemistry

• Validation in bacterial growth assays against priority pathogens

• Synergy studies with established antibiotics

• Assessment of resistance development potential

What role does M. infernorum uppP play in bacterial cell wall biosynthesis compared to the related enzyme UPPS?

M. infernorum uppP and UPPS represent different but complementary enzymatic activities in the bacterial cell wall biosynthesis pathway:

Enzymatic Functions:

Pathway Integration:
The two enzymes function in a cyclical pathway where UPPS synthesizes undecaprenyl diphosphate, which after several transformations and use in peptidoglycan assembly, is recycled through the action of uppP . This creates a continuous supply of the essential lipid carrier needed for cell wall synthesis.

Inhibitor Profiles:
UPPS inhibitors have shown promising antibacterial activity against Gram-positive pathogens including MRSA, VRE, and B. anthracis with MIC values in the 0.25–4 μg/mL range . The most effective UPPS inhibitor identified in recent research (compound 1, a rhodanine derivative) demonstrated strong synergism with methicillin against MRSA . Similar studies with uppP inhibitors would be valuable to understand comparative efficacy and resistance profiles.

What ecological insights can be gained from studying M. infernorum and its enzymes like uppP?

Study of M. infernorum and its enzymes provides valuable ecological insights:

Methanotrophic Diversity:
M. infernorum represents a non-proteobacterial methanotroph that employs an autotrophic lifestyle, using methane solely for energy generation rather than as a carbon source . This metabolic strategy differs fundamentally from the more well-studied proteobacterial methanotrophs and expands our understanding of methane cycling in natural environments.

Detection in Environmental Samples:
Traditional methods for detecting methanotrophs in environmental samples, such as 13CH4-stable isotope probing (SIP) and proteobacterial pmoA-targeted PCR, fail to detect verrucomicrobial methanotrophs like M. infernorum . This suggests these organisms may have been overlooked in previous environmental studies, potentially underestimating their contribution to methane cycling.

Adaptation to Extreme Environments:
The enzymes of M. infernorum, including uppP, possess adaptations enabling function under acidic, high-temperature conditions typical of geothermal environments . These adaptations provide insights into molecular evolution and protein stability mechanisms in extreme conditions.

Methodological Implications:
Modified techniques such as 13CO2-SIP combined with verrucomicrobial-pmoA-targeted qPCR have proven effective in detecting these autotrophic methanotrophs in environmental samples . This methodological advancement allows more comprehensive ecological studies of methanotrophic communities.

Carbon Cycling Impact:
Understanding the role of autotrophic methanotrophs like M. infernorum in both methane oxidation and carbon fixation provides a more complete picture of carbon cycling in specialized environments and may have implications for climate change research.

How might the extremophilic origin of M. infernorum affect the properties and potential applications of its uppP enzyme?

The extremophilic nature of M. infernorum confers unique characteristics to its enzymes, including uppP, with several implications for research and applications:

Structural Adaptations and Stability:
M. infernorum thrives in acidic, high-temperature geothermal environments , suggesting its enzymes possess adaptations for stability under these conditions. The uppP enzyme likely features:

• Increased hydrophobic core packing

• Additional salt bridges and hydrogen bonding networks

• Reduced surface loop flexibility

• Potentially unique amino acid composition favoring acidic residue substitutions

Experimental Considerations:
When designing experiments with M. infernorum uppP, researchers should consider:

• Expanded pH optima testing (pH 2-7) to identify acidic activity profiles

• Temperature stability assays (37-80°C) to characterize thermostability

• Buffer systems that maintain pH stability at elevated temperatures

• Potential metal ion dependencies that differ from mesophilic homologs

Biotechnological Applications:
The unique properties of M. infernorum uppP may prove valuable for:

• Development of enzymes functional in industrial processes requiring acidic conditions

• Creation of thermostable enzymatic tools for molecular biology

• Engineering enhanced stability into homologous enzymes through directed evolution

• Exploration as biocatalysts in pharmaceutical synthesis requiring robust enzymes

Comparative Studies:
A systematic comparison between M. infernorum uppP and homologs from mesophilic bacteria would elucidate:

• Key residues responsible for acid tolerance

• Structural elements conferring thermostability

• Evolutionary adaptations at the molecular level

• Structure-function relationships in the undecaprenyl-diphosphatase family

What experimental design considerations are critical when developing screening assays for M. infernorum uppP inhibitors?

Development of robust screening assays for M. infernorum uppP inhibitors requires careful consideration of multiple experimental parameters:

Assay Development Strategy:
Following established experimental design principles , a systematic approach should include:

• Objective Definition:

  • Clear determination whether the goal is to maximize inhibition, identify specific mechanism inhibitors, or develop selective inhibitors

• Process Definition and Factor Selection:

  • Identification of critical variables affecting assay performance

  • Consideration of enzyme concentration, substrate concentration, pH, temperature, buffer composition, and detection method

  • Selection of practical, feasible factors that can be effectively controlled

• Response Selection and Measurement System:

  • Implementation of a reliable detection system (colorimetric, fluorescent, or radiometric)

  • Validation of measurement accuracy, repeatability, and reproducibility

  • Ensuring sample representativeness from each experimental run

• Design Selection:

  • Initially employing screening designs to explore multiple factors

  • Progressing to response surface methodology for optimization

  • Incorporating controls for non-specific inhibition and interference

Critical Parameters Table:

Validation and Quality Control:

• Implementation of Z' factor determination to assess assay quality

• Inclusion of known phosphatase inhibitors as positive controls

• Development of orthogonal assays to confirm initial hits

• Testing for compound interference with detection systems

How can advanced structural biology techniques be applied to understand the mechanism of M. infernorum uppP and facilitate structure-based inhibitor design?

Advanced structural biology techniques offer powerful approaches to elucidate M. infernorum uppP mechanisms and guide inhibitor design:

Cryo-Electron Microscopy (Cryo-EM):

• Advantage: Allows visualization of membrane proteins in near-native environments without crystallization

• Application: Determination of uppP structure in nanodiscs or detergent micelles

• Challenge: Relatively small size of uppP may require innovative approaches like multimerization or antibody fragment complexation

• Expected outcome: Medium to high-resolution structures revealing transmembrane topology and substrate binding sites

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

• Advantage: Maps protein dynamics and ligand-induced conformational changes

• Application: Identification of regions involved in substrate binding and catalysis

• Challenge: Membrane protein analysis requires specialized detergent compatibility

• Expected outcome: Conformational dynamics data complementing static structural information

Molecular Dynamics Simulations:

• Advantage: Provides atomic-level insights into protein motion and ligand interactions

• Application: Modeling of enzyme-substrate complexes and inhibitor binding modes

• Challenge: Accurate parameterization of membrane environment

• Expected outcome: Identification of transient binding pockets and catalytic mechanism details

Structure-Based Drug Design Workflow:

• Generate comprehensive structural model through integration of multiple techniques

• Identify and characterize binding pockets using computational analysis

• Perform virtual screening against identified pockets

• Select diverse candidates for biochemical validation

• Determine structure-activity relationships of initial hits

• Optimize lead compounds based on structural insights

• Validate binding modes through co-crystallization or NMR studies

Innovative Approaches:

• Serial femtosecond crystallography using X-ray free-electron lasers for microcrystals

• Native mass spectrometry for studying intact membrane protein-ligand complexes

• Solid-state NMR for structural analysis in lipid environments

• Integrative structural biology combining multiple techniques for comprehensive modeling

What are the main challenges in working with recombinant M. infernorum uppP and how can they be addressed?

Working with recombinant M. infernorum uppP presents several challenges typical of membrane proteins from extremophilic organisms:

Protein Expression Challenges:

Purification Challenges:

Activity Assay Challenges:

How can researchers effectively design experiments to investigate the role of M. infernorum uppP in antibiotic resistance?

Designing experiments to investigate M. infernorum uppP's role in antibiotic resistance requires a systematic experimental design approach:

Fundamental Experimental Design Process:
Following established design principles , researchers should:

• Define Clear Objectives:

  • Determine specific hypotheses regarding uppP's contribution to resistance

  • Establish quantifiable metrics for resistance evaluation

  • Define success criteria for experimental outcomes

• Select Appropriate Experimental System:

  • Choose relevant bacterial strains (model organisms, clinical isolates)

  • Select antibiotics targeting cell wall synthesis

  • Determine appropriate growth conditions mimicking relevant environments

• Implement Multi-Level Experimental Approach:

Genetic Manipulation Studies:

• Generate uppP knockdown/knockout strains (if viable)

• Create uppP overexpression strains

• Develop site-directed mutants targeting key catalytic residues

• Measure changes in antibiotic susceptibility profiles using standardized methods

Biochemical Characterization:

• Determine kinetic parameters of wild-type and mutant uppP variants

• Assess inhibition profiles with various antibiotics

• Measure enzyme activity in membrane preparations from antibiotic-resistant vs. sensitive strains

• Quantify undecaprenyl phosphate levels in resistant vs. sensitive strains

Antibiotic Synergy Studies:

• Conduct checkerboard assays with uppP inhibitors and conventional antibiotics

• Calculate fractional inhibitory concentration indices (FICI) to quantify synergistic, additive, or antagonistic effects

• Generate isobolograms to visualize interaction patterns as demonstrated for other cell wall synthesis inhibitors

• Test combinations against resistant clinical isolates

Resistance Development Assessment:

• Perform sequential passage experiments with uppP inhibitors

• Monitor resistance emergence rates compared to conventional antibiotics

• Characterize resistance mechanisms through whole genome sequencing

• Assess cross-resistance profiles between different inhibitor classes

• Statistical Design Considerations:

  • Implement appropriate replication (biological and technical)

  • Include relevant controls (vehicle, unrelated antibiotics)

  • Use statistical models appropriate for the data type

  • Consider screening designs for initial studies followed by optimization designs

• Data Integration and Interpretation:

  • Correlate genetic, biochemical, and microbiological data

  • Develop mechanistic models explaining resistance phenotypes

  • Compare results with known resistance mechanisms for other cell wall targeting antibiotics

  • Validate findings across multiple bacterial species if possible

What are the critical considerations for translating in vitro findings about M. infernorum uppP to potential therapeutic applications?

Translating in vitro findings about M. infernorum uppP to therapeutic applications involves navigating several critical considerations:

Target Validation and Druggability Assessment:

The undecaprenyl diphosphate pathway has demonstrated validity as an antibiotic target, with existing compounds showing promising activity against important pathogens . Key considerations include:

• Confirming essentiality of uppP function across target pathogens

• Assessing the degree of sequence and functional conservation between M. infernorum uppP and homologs in pathogenic bacteria

• Identifying unique structural features that can be exploited for selective inhibition

• Evaluating the presence of potential compensatory mechanisms in target organisms

Inhibitor Development Pipeline:

Synergistic Approaches:

Compounds targeting the cell wall biosynthesis pathway have shown synergistic effects with existing antibiotics, as demonstrated by the FICI value of 0.11 for a UPPS inhibitor combined with methicillin against MRSA . Translational considerations should include:

• Systematic evaluation of uppP inhibitors in combination with established antibiotics

• Prioritization of combinations showing strong synergism (FICI < 0.5)

• Development of appropriate formulations for combination therapy

• Regulatory strategy for combination product approval

Resistance Management Strategy:

To address potential resistance development:

• Characterize resistance mechanisms through laboratory evolution studies

• Assess cross-resistance with other cell wall targeting antibiotics

• Develop inhibitors targeting multiple steps in the pathway simultaneously

• Consider designing multi-targeting molecules with activity against both uppP and related enzymes

Biological Context Translation:

The extremophilic origin of M. infernorum uppP requires careful consideration when translating findings to therapeutic contexts:

• Evaluate activity of inhibitors against homologous enzymes from pathogenic bacteria

• Confirm target engagement in cellular systems under physiologically relevant conditions

• Assess potential off-target effects on human enzymes

• Consider the impact of different membrane compositions on inhibitor efficacy