Recombinant Pseudomonas syringae pv. syringae Large-conductance mechanosensitive channel (mscL)

How does the gating mechanism of P. syringae mscL differ from other bacterial mechanosensitive channels?

The gating process of P. syringae mscL involves large conformational changes as it transitions from the closed state to the open state through several intermediates. In the open state, the channel dilates its central pore to approximately 30 Å, becoming permeable to water, ions, metabolites, and even small proteins .

An iris-like open-state model has been proposed based on computational modeling and disulfide cross-linking data. This model has been verified and revised through electron paramagnetic resonance spectroscopy and electrostatic repulsion tests. Recent studies using native ion mobility-mass spectrometry have demonstrated that MscL has the inherent structural flexibility to achieve large global structural changes even in the absence of a lipid bilayer .

What distinguishes P. syringae mscL is that only the top part of the C-terminal domain (from residue A110 to E118) dissociates during channel gating, while the rest of the C-terminus remains assembled. This is consistent with the view that the C-terminus functions as a molecular sieve and stabilizer of the oligomeric MscL structure .

What experimental techniques are commonly used to study recombinant P. syringae mscL?

Several complementary techniques are employed to study the structure and function of recombinant P. syringae mscL:

Researchers typically employ a combination of these methods to gain comprehensive insights into the structure-function relationships of mscL.

How can recombineering techniques be optimized for studying mscL function in Pseudomonas syringae?

Recombineering in P. syringae can be optimized using the RecTE homologs identified in P. syringae pv. syringae B728a. These proteins are similar to the RecE/RecT proteins of the Rac prophage and lambda Red Exo and Beta, and promote efficient homologous recombination between genomic loci and linear DNA substrates introduced by electroporation .

The methodology involves:

• Vector Construction: Create expression vectors containing the P. syringae recT (recTPsy) and recTE (recTEPsy) genes. For example, vectors like pUCP24/47 can be used, which contain the BAD nptII promoter for constitutive expression .

• Transformation Protocol: Transform P. syringae cells with the expression vectors using electroporation. The RecT homolog alone is sufficient for recombination of single-stranded DNA oligonucleotides, while efficient recombination of double-stranded DNA requires both RecT and RecE homologs .

• Selection Strategy: Incorporate counterselectable markers like the B. subtilis sacB gene into expression vectors to expedite plasmid elimination after recombination is complete .

• Verification: Confirm successful recombineering through DNA sequencing and functional assays of the modified mscL gene.

This approach allows for targeted gene disruptions, point mutations, or replacements in the mscL gene, enabling detailed structure-function studies.

What are the structural dynamics of the C-terminal domain during mscL gating, and how can they be experimentally verified?

The C-terminal domain of MscL undergoes specific structural changes during channel gating. Experimental evidence combined with computational modeling demonstrates that only the top portion (residues A110 to E118) of the C-terminal domain dissociates during gating, while the remainder stays assembled .

To experimentally verify these dynamics:

• SDSL EPR Spectroscopy: This technique has been successfully used to determine both closed and open channel structures in lipid bilayers. By introducing spin labels at specific residues throughout the C-terminal domain, researchers can monitor changes in mobility and proximity relationships during gating .

• Cross-linking Studies: Strategic introduction of cysteine residues for disulfide cross-linking can test specific hypotheses about which parts of the structure remain associated during gating.

• Molecular Dynamics Simulations: These computational approaches can model the energetics and kinetics of structural transitions and generate testable hypotheses about the behavior of specific residues.

• Native Ion Mobility-Mass Spectrometry: This technique has demonstrated that MscL has inherent structural flexibility even in the absence of a lipid bilayer, providing insights into the conformational states accessible to the channel .

The key finding that only the top part of the C-terminal domain dissociates during gating supports the hypothesis that the C-terminus functions as both a molecular sieve and a stabilizer of the pentameric structure .

How do point mutations in the transmembrane domains affect the mechanosensitivity of P. syringae mscL?

While specific data on P. syringae mscL mutations is limited in the provided search results, research on mechanosensitive channels generally indicates that transmembrane domains play critical roles in sensing membrane tension and channel gating.

To investigate the effects of point mutations:

• Recombineering Approach: Use the RecTE-based recombineering system described in search result to introduce specific point mutations in the transmembrane domains of the mscL gene.

• Electrophysiological Characterization: Employ patch-clamp techniques to measure the pressure threshold for channel opening, conductance, and gating kinetics of the mutant channels compared to wild-type.

• Computational Modeling: Use molecular dynamics simulations to predict how specific mutations might alter the mechanical properties of the transmembrane helices and their interaction with the lipid bilayer.

• In vivo Functional Assays: Test the ability of mutant channels to protect cells from osmotic shock. This could involve subjecting bacteria expressing different mscL variants to hypoosmotic shock and measuring survival rates.

• Structural Studies: Use techniques like X-ray crystallography (as shown in the crystal data table below) or SDSL EPR to determine how mutations affect the structure of the channel in both closed and open states.

What are the differences in mscL function between pathogenic and beneficial strains of P. syringae?

P. syringae strains exhibit diverse behaviors, ranging from plant-pathogenic to plant-beneficial. While search result describes differences between pathogenic strains like P. syringae pv. tomato DC3000 and potentially beneficial strains like P. syringae strain 260-02, specific information about mscL function differences is not directly addressed.

To investigate potential differences in mscL function between pathogenic and beneficial strains:

• Comparative Genomic Analysis: Compare the mscL gene sequences and regulatory regions across multiple strains with different plant interactions. Look for polymorphisms that might affect channel function or expression.

• Expression Studies: Quantify mscL expression levels under various osmotic conditions in different strains using qRT-PCR or RNA-seq approaches.

• Functional Characterization: Express recombinant mscL proteins from different strains and compare their electrophysiological properties, including pressure thresholds, conductance, and gating kinetics.

• Strain-Specific Phenotypes: Test osmotic shock resistance in different strains and correlate with mscL sequence variations. Use the recombineering techniques described in search result to swap mscL alleles between strains to determine if differences in osmotic resistance are linked to the mscL gene.

• Host-Interaction Studies: Investigate whether mscL function contributes to survival during plant colonization or infection by comparing wild-type and mscL mutant strains in plant models.

Search result notes that strain 260-02 has a distinct volatile emission profile and different plant-colonization pattern compared to strain DC3000, despite great similarity at the genomic level. It would be valuable to determine if differences in mechanosensitive channel function contribute to these phenotypic differences.

How can research questions about P. syringae mscL be effectively formulated for a systematic review?

Formulating effective research questions for a systematic review of P. syringae mscL follows specific methodological principles:

• Use the PICO-TSS Framework:

  • P: Population (e.g., Pseudomonas syringae strains)

  • I: Intervention (e.g., recombinant expression of mscL)

  • C: Control (e.g., wild-type mscL)

  • O: Outcome (e.g., osmotic stress resistance)

  • T: Time (e.g., studies from 2000-2025)

  • S: Study design (e.g., experimental studies)

  • S: Setting (e.g., in vitro or in planta experiments)

• Identify Knowledge Gaps: Start by examining the universal knowledge through comprehensive searches (e.g., PubMed, PROSPERO) to identify areas of uncertainty .

• Develop a Hypothesis-Driven Question: Refine your primary question based on the knowledge gap identified. For example: "Does recombinant expression of mscL from P. syringae enhance osmotic stress tolerance compared to wild-type expression?"

• Apply the FINER Criteria: Ensure your question is:

  • Feasible

  • Interesting

  • Novel

  • Ethical

  • Relevant

• Refine Through Cycles: Use the "infinity circles of question generation" approach (Figure 3 in search result ) to continuously refine your question based on preliminary findings.

An example of a well-formulated systematic review question might be: "What structural and functional differences exist between mscL proteins from pathogenic versus beneficial strains of Pseudomonas syringae, and how do these differences contribute to osmotic stress responses in plant-associated environments?"

What role does the mscL channel play in antibiotic resistance in P. syringae?

While specific information about mscL's role in antibiotic resistance in P. syringae is not directly addressed in the search results, search result mentions that "recent studies suggest that the open pore of MscL permits entry of streptomycin and could potentially serve as a target for antimicrobial agents" .

To investigate this relationship, researchers could:

• Antibiotic Uptake Studies: Use fluorescently labeled antibiotics to determine if they enter bacterial cells through mscL channels during osmotic downshock when channels are likely to be open.

• Resistance Development: Compare the development of antibiotic resistance in wild-type strains versus strains with modified mscL genes (using the recombineering techniques described in search result ).

• Structural Determinants: Identify which regions of the mscL channel influence antibiotic permeation by generating targeted mutations and testing antibiotic sensitivity.

• Expression Regulation: Investigate whether exposure to antibiotics affects mscL expression levels, potentially as part of a stress response.

• Combination Therapies: Test whether compounds that activate mscL channels can enhance the efficacy of antibiotics against P. syringae by increasing cellular uptake.

This area represents an important intersection between basic research on mechanosensitive channel function and applied research on bacterial pathogenicity and antibiotic resistance mechanisms.

What are the most effective methods for expressing and purifying recombinant P. syringae mscL for structural studies?

Based on search result , the recombinant full-length P. syringae pv. syringae mscL protein can be successfully expressed in E. coli with an N-terminal His-tag. The following methodological approach is recommended for expression and purification:

• Expression System:

  • Host: E. coli

  • Vector: Expression vector containing an N-terminal His-tag

  • Protein Length: Full length (1-148 amino acids)

  • Expression Conditions: Optimize temperature, IPTG concentration, and induction time

• Purification Protocol:

  • Lyse cells under native conditions

  • Purify using nickel affinity chromatography

  • Further purify by size exclusion chromatography if higher purity is required

  • Final purity should be greater than 90% as determined by SDS-PAGE

• Storage and Handling:

  • Store at -20°C/-80°C

  • Aliquot to avoid repeated freeze-thaw cycles

  • Use Tris/PBS-based buffer with 6% Trehalose at pH 8.0

  • 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

• Quality Control:

  • Verify protein identity by mass spectrometry

  • Confirm structural integrity using circular dichroism

  • Test functionality through liposome-reconstitution assays

For structural studies specifically, additional considerations include:

• Membrane Protein Crystallization:

  • Screen various detergents for optimal solubilization

  • Use lipidic cubic phase or bicelle crystallization methods

  • Consider co-crystallization with antibody fragments to enhance crystallization

  • Refer to the crystal data parameters in search result as a starting point

This approach has been successfully used to obtain high-quality recombinant MscL protein suitable for structural and functional studies.