Recombinant Yersinia pestis bv. Antiqua Disulfide bond formation protein B (dsbB)

What is the function of Disulfide bond formation protein B (dsbB) in Yersinia pestis?

Disulfide bond formation protein B (DsbB) in Yersinia pestis is an inner membrane protein that functions as a critical component of the bacterial disulfide bond formation pathway. DsbB oxidizes DsbA, which in turn catalyzes disulfide bond formation in periplasmic proteins . This oxidative folding system is essential for proper protein folding and stability in the periplasmic space. In Y. pestis specifically, DsbB plays a significant role in biofilm formation regulation, which is crucial for flea-to-mammal transmission of plague . Mutations in dsbB lead to increased biofilm formation, suggesting that DsbB normally functions to maintain redox homeostasis that regulates biofilm development processes .

How does the structure of DsbB relate to its function in bacterial membranes?

DsbB is an integral membrane protein embedded in the bacterial inner membrane with multiple transmembrane domains. High-resolution structural analysis combining X-ray crystallography and solid-state NMR has revealed that DsbB contains four transmembrane helices arranged to form a compact fold within the lipid bilayer . These structural features position reactive cysteine residues optimally for electron transfer reactions.

The structural arrangement of DsbB allows it to interact with both the membrane environment and its substrate DsbA. When embedded in phospholipid bilayers (such as POPE, which mimics bacterial membranes), DsbB adopts a conformation that facilitates the oxidation-reduction cascade necessary for disulfide bond formation . This membrane topology is critical for its function, as it connects the periplasmic redox state with cytoplasmic processes.

What is the relationship between DsbB and biofilm formation in Yersinia pestis?

Research has demonstrated a significant inverse relationship between DsbB activity and biofilm formation in Y. pestis. When dsbB is mutated or inactivated, Y. pestis shows substantially increased biofilm formation . This phenomenon occurs because:

• DsbB normally contributes to maintaining an oxidizing environment in the periplasm

• In a dsbB mutant, the periplasmic environment becomes more reducing

• This reducing environment triggers increased activity of the HmsD diguanylate cyclase

• Enhanced HmsD activity leads to higher intracellular cyclic-di-GMP (c-di-GMP) levels

• Elevated c-di-GMP promotes biofilm formation

Experimental evidence shows that intracellular c-di-GMP levels are significantly higher in dsbB mutants compared to wild-type strains . This indicates that DsbB indirectly regulates biofilm formation by influencing the redox state, which affects signaling pathways controlling biofilm development. This connection is particularly important for understanding Y. pestis transmission, as biofilm formation in the flea proventriculus enhances plague transmission to mammals .

How do mutations in DsbB affect the redox-sensing mechanisms in Y. pestis biofilm regulation?

Mutations in DsbB create a more reducing periplasmic environment that significantly alters Y. pestis biofilm regulation through a complex signaling cascade involving the HmsCDE system. In wild-type Y. pestis, DsbB maintains an oxidizing periplasm that supports appropriate disulfide bond formation . When dsbB is mutated, the following molecular events occur:

• The periplasmic redox potential shifts toward a more reducing state

• This reducing environment affects the HmsC protein (part of the HmsCDE system)

• HmsC undergoes conformational changes due to altered disulfide bonding

• These changes modify HmsC's regulatory effect on HmsD (a diguanylate cyclase)

• HmsD becomes more active, synthesizing increased amounts of c-di-GMP

• Elevated c-di-GMP levels stimulate biofilm formation mechanisms

Experimental data shows that a dsbB mutant exhibits significantly increased cellular c-di-GMP levels compared with the parent strain, similar to patterns observed in dsbA mutants . Importantly, adding oxidizing agents such as CuSO₄ can suppress the enhanced biofilm formation in dsbB mutants by restoring a more oxidizing environment, confirming the redox-dependent nature of this regulatory mechanism .

What are the structural differences between DsbB proteins from Y. pestis and E. coli, and how might these differences impact function?

While the search results don't provide direct structural comparisons between Y. pestis and E. coli DsbB, we can infer potential differences based on available structural data and evolutionary considerations:

The structural differences, although subtle, may reflect adaptations to the specific physiological conditions encountered by Y. pestis during its infectious cycle, particularly in relation to biofilm formation in the flea vector. These differences could potentially be targeted for species-specific therapeutic development.

How does the HmsCDE system integrate redox sensing with biofilm regulation in Y. pestis?

The HmsCDE system in Y. pestis acts as a sophisticated redox-responsive regulatory network that modulates biofilm formation through controlled synthesis of cyclic-di-GMP. Research has revealed several key mechanisms in this integration:

• HmsC functions as a redox sensor protein that responds to changes in periplasmic redox state

• Under oxidizing conditions (normal DsbB function), HmsC adopts a conformation that inhibits HmsD activity

• Under reducing conditions (dsbB mutation), HmsC's inhibitory effect on HmsD is diminished

• HmsD, relieved from inhibition, increases c-di-GMP synthesis

• HmsE appears to function as a modulatory component in this regulatory circuit

Experimental evidence demonstrates that in a dsbA mutant (which simulates a reducing environment), biofilm formation increases in an HmsD-dependent manner . Additionally, intracellular c-di-GMP levels are significantly elevated in dsbA mutants compared to wild-type strains, but this increase is eliminated in an hmsD mutant background . This indicates that HmsD is the primary diguanylate cyclase responding to redox changes.

Western blot analysis shows that protein levels of HmsC, HmsD, and HmsE are not significantly affected by dsbA mutation, suggesting that the regulatory mechanism operates at the functional rather than expressional level . The system has evolved to respond quickly to environmental redox changes, potentially allowing Y. pestis to adapt to different host environments.

What are the optimal methods for purifying recombinant Y. pestis DsbB for structural studies?

Purification of recombinant Y. pestis DsbB for structural studies requires specialized approaches due to its membrane-embedded nature. Based on successful structural studies of related proteins, the following methodology is recommended:

• Expression system selection:

  • Bacterial expression using E. coli host strains lacking endogenous DsbB (ΔdsbB) to prevent interference

  • Consider fusion tags that enhance expression and solubility while allowing detection and purification

• Optimized expression protocol:

  • Induce expression at lower temperatures (16-22°C) for extended periods (12-24 hours) to facilitate proper membrane integration

  • Use arabinose-inducible promoters for fine control of expression levels, similar to the system used for HmsD (0.02% arabinose induction for 12h at 22°C)

• Membrane extraction and solubilization:

  • Harvest cells and resuspend in PBS supplemented with protease inhibitor cocktail

  • Disrupt cells via sonication or cell disruption systems

  • Isolate membrane fractions through differential centrifugation

  • Solubilize membranes with mild detergents (n-dodecyl-β-D-maltopyranoside or n-octyl-β-D-glucopyranoside)

• Purification steps:

  • Immobilized metal affinity chromatography using Ni-NTA resin for His-tagged proteins

  • Size exclusion chromatography to separate properly folded protein from aggregates

  • Consider lipid nanodiscs or amphipols for stabilization in a membrane-like environment

• Quality assessment:

  • Western blotting to confirm identity and purity

  • Circular dichroism to verify secondary structure

  • Functional assays to confirm redox activity

This methodology has been adapted from successful approaches used for related membrane proteins, including the purification protocols described for HmsD and structural studies of DsbB proteins .

How can the redox state of DsbB be effectively measured in experimental conditions?

Measuring the redox state of DsbB requires techniques that can distinguish between oxidized and reduced forms of the protein's catalytic cysteine residues. The following methodological approaches are recommended:

• Alkylation-based assays:

  • Treat samples with alkylating agents (iodoacetamide or N-ethylmaleimide) that covalently modify free thiols

  • Analyze by non-reducing SDS-PAGE to visualize mobility shifts between oxidized and reduced forms

  • Quantify band intensities to determine the ratio of oxidized to reduced protein

• Fluorescent thiol labeling:

  • Use thiol-reactive fluorescent probes that selectively bind to reduced cysteines

  • Quantify fluorescence intensity to determine the proportion of reduced protein

  • This approach allows for in situ visualization when combined with microscopy

• Mass spectrometry-based approaches:

  • Employ differential alkylation with isotopically labeled reagents

  • Digest protein and analyze peptide fragments by LC-MS/MS

  • Identify specific cysteine residues involved in disulfide bonding

  • Quantify relative abundance of oxidized versus reduced peptides

• Electrochemical methods:

  • Use protein film voltammetry to directly measure the redox potential of purified DsbB

  • This approach provides thermodynamic parameters of the redox reactions

• Genetic reporter systems:

  • Engineer fusion proteins linking DsbB redox state to fluorescent protein activity

  • Monitor fluorescence as a proxy for redox state in living cells

When applying these methods to experimental investigations of Y. pestis DsbB, it's important to maintain anaerobic conditions during sample preparation to prevent artificial oxidation. The redox state measurements should be calibrated using controls with known oxidation states, such as samples treated with strong oxidants (CuSO₄) or reductants (DTT) .

What molecular dynamics simulation approaches are most effective for studying DsbB membrane integration?

Molecular dynamics (MD) simulations provide valuable insights into the behavior of membrane proteins like DsbB within lipid bilayers. Based on successful applications with related proteins, the following MD simulation approach is recommended:

• System preparation:

  • Start with a high-resolution structure derived from X-ray crystallography and/or solid-state NMR

  • Embed the protein in a POPE bilayer to mimic the bacterial inner membrane environment

  • Solvate the system with explicit water molecules and add counterions to neutralize the system

  • The combined experimental and computational approach has proven effective for DsbB structural studies

• Force field selection:

  • Use specialized force fields optimized for membrane proteins (CHARMM36 for lipids and protein)

  • Employ parameters specifically refined for disulfide bonds and redox-active cysteines

• Simulation protocol:

  • Perform energy minimization followed by careful equilibration steps:
    a. Position-restrained equilibration (gradually releasing constraints)
    b. Temperature equilibration using temperature coupling algorithms
    c. Pressure equilibration to achieve proper bilayer properties

  • Conduct production runs on microsecond timescales to observe relevant conformational changes

• Advanced sampling techniques:

  • Implement replica exchange methods to enhance conformational sampling

  • Use steered MD or umbrella sampling to study specific processes like substrate binding

• Analysis approaches:

  • Calculate order parameters for lipid interactions

  • Analyze protein stability through RMSD and RMSF calculations

  • Identify water penetration and hydrogen bonding networks

  • Characterize cysteine redox microenvironments

The effectiveness of this approach is supported by successful MD simulations of membrane proteins where the structural models were validated by experimental data . For example, the joint calculation of DsbB structure using X-ray reflections and solid-state NMR data produced models with significantly improved backbone RMSD (reduced from 2.36 Å to 1.35 Å) .

How should researchers interpret contradictory findings on DsbB function in different bacterial species?

When confronted with contradictory findings regarding DsbB function across different bacterial species, researchers should employ a systematic approach to data interpretation:

• Consider evolutionary context:

  • DsbB proteins share conserved functional domains but may have evolved species-specific adaptations

  • Y. pestis DsbB may have unique features related to its lifecycle alternating between flea vectors and mammalian hosts

  • Phylogenetic analysis can help determine if functional differences correlate with evolutionary distance

• Examine experimental conditions:

  • Different growth conditions (temperature, media composition, oxygen availability) can significantly affect DsbB function

  • Y. pestis biofilm formation is notably temperature-dependent, and redox sensing may be calibrated differently at flea (22°C) versus mammalian (37°C) temperatures

  • Standardize experimental conditions when making cross-species comparisons

• Consider system complexity:

  • The DsbB-DsbA system interacts with species-specific downstream targets

  • In Y. pestis, the unique interaction with the HmsCDE system creates a specialized redox-responsive regulatory network

  • Construct a comprehensive model incorporating all known interaction partners

• Analyze genetic background effects:

  • The phenotypic effects of dsbB mutations may depend on the genetic background

  • Creation of isogenic mutants in different species can help resolve apparent contradictions

• Quantitative versus qualitative differences:

  • What appears as a contradiction may reflect quantitative differences in similar mechanisms

  • Use quantitative measurements of redox potential, protein activity, and phenotypic outcomes

When interpreting data specific to Y. pestis DsbB, pay particular attention to its relationship with biofilm formation and c-di-GMP signaling. The data showing that dsbB mutation increases biofilm formation in Y. pestis may seem contradictory to findings in other species where DsbB is essential for biofilm formation, but this likely reflects the specialized integration of DsbB into Y. pestis-specific regulatory networks .

What statistical approaches are most appropriate for analyzing DsbB redox state data in relation to biofilm formation?

Analyzing the relationship between DsbB redox state and biofilm formation requires robust statistical approaches due to the complex, non-linear nature of biological responses to redox changes. The following statistical methods are recommended:

• Correlation analysis:

  • Pearson or Spearman correlation coefficients to quantify relationships between redox state and biofilm metrics

  • Calculate correlation matrices including multiple variables (redox potential, c-di-GMP levels, biofilm mass)

  • Test for non-linear relationships using polynomial regression models

• Multivariate analysis:

  • Principal Component Analysis (PCA) to identify patterns in multidimensional data

  • Partial Least Squares (PLS) regression to model the relationship between redox measurements and biofilm parameters

  • These approaches can reveal complex relationships not apparent in univariate analyses

• Time-series analysis:

  • Apply time-series statistical methods to analyze the temporal dynamics of redox state changes and subsequent biofilm development

  • Use autocorrelation functions to identify temporal patterns and delays between redox changes and biofilm responses

• Bayesian approaches:

  • Develop Bayesian network models to infer causal relationships in the redox-biofilm pathway

  • Incorporate prior knowledge about the HmsCDE system into model parameters

• Appropriate controls and replication:

  • Include biological replicates (n ≥ 3) for robust statistical analysis, as demonstrated in intracellular c-di-GMP measurement studies

  • Use appropriate positive and negative controls (e.g., dsbA mutants, chemical redox modulators)

  • Report results as means with standard deviations or standard errors

When reporting statistical significance, follow the example shown in Figure 2 of the research on intracellular c-di-GMP levels, where significance levels are clearly indicated (P < 0.01) and results are presented as means with standard deviations from three independent experiments .

How can researchers reconcile structural data obtained from different experimental techniques for a comprehensive model of DsbB?

Creating a comprehensive structural model of DsbB requires integrating data from multiple experimental techniques, each with distinct strengths and limitations. A systematic approach to data reconciliation includes:

• Hierarchical data integration:

  • Begin with high-resolution X-ray crystallography data to establish the core structure

  • Enhance with solid-state NMR data to resolve dynamic regions and membrane interfaces

  • Refine through molecular dynamics simulations in explicit membrane environments

  • This combined approach has been successfully applied to DsbB structural studies, reducing average backbone RMSD from 2.36 Å (X-ray alone) to 1.35 Å (X-ray + SSNMR)

• Weighted constraint approach:

  • Assign confidence weights to constraints from different experimental sources

  • Implement joint refinement protocols in structural calculation software like Xplor-NIH

  • The statistical comparison in Table 1 demonstrates significant improvement in structure quality metrics when combining X-ray and NMR data :

• Cross-validation methods:

  • Reserve a subset of experimental data for validation rather than refinement

  • Calculate cross-validation metrics (R-free in crystallography, NOE violations in NMR)

  • Use these metrics to prevent overfitting and assess model reliability

• Ensemble representation:

  • Present the final model as an ensemble that captures conformational flexibility

  • Quantify uncertainty in different regions of the structure

  • Identify regions with high confidence versus those requiring further investigation

• Functional validation:

  • Test structural predictions through mutagenesis of key residues

  • Correlate structural features with functional measurements like redox activity

  • Ensure the model explains species-specific functional differences

This integrated approach acknowledges that no single experimental technique provides complete structural information for membrane proteins like DsbB. By combining complementary methods and validating against functional data, researchers can develop comprehensive models that provide mechanistic insights into DsbB function in Y. pestis.

What are the most promising approaches for targeting DsbB in Y. pestis for potential therapeutic development?

The critical role of DsbB in Y. pestis pathogenicity and biofilm formation makes it an attractive target for novel therapeutic development. Several promising research approaches include:

• Structure-based inhibitor design:

  • Utilize the refined structural models combining X-ray crystallography and NMR data to identify binding pockets unique to Y. pestis DsbB

  • Design small molecules that can specifically disrupt the DsbB-DsbA interaction or directly inhibit DsbB catalytic activity

  • Computational methods including molecular docking and virtual screening can accelerate this process

• Redox-active compounds:

  • Develop compounds that disrupt the normal redox cycling of DsbB

  • Target the specific cysteine pairs involved in electron transfer

  • Design redox-active molecules that become trapped in the DsbB active site

• Peptide inhibitors:

  • Design peptide mimetics based on the DsbA-DsbB interaction interface

  • Develop cell-penetrating peptides that can access the periplasmic space

  • Use phage display libraries to identify peptides with high affinity for Y. pestis DsbB

• Allosteric modulators:

  • Target non-catalytic regions that influence DsbB conformation and activity

  • Focus on regions that may differ between Y. pestis and human host proteins

  • Identify compounds that stabilize inactive conformations of DsbB

• Combination approaches:

  • Target multiple components of the disulfide bond formation pathway simultaneously

  • Develop dual inhibitors that affect both DsbB and the HmsCDE system

  • This approach could provide synergistic effects and reduce resistance development

How can advanced imaging techniques be applied to study DsbB localization and dynamics during biofilm formation?

Advanced imaging techniques offer powerful approaches to investigate DsbB localization and dynamics during Y. pestis biofilm formation. Promising methodological directions include:

• Super-resolution microscopy:

  • Apply techniques such as PALM, STORM, or STED to visualize DsbB distribution in bacterial membranes

  • Achieve nanoscale resolution of DsbB clustering during different stages of biofilm development

  • Combine with specific fluorescent tags for DsbB, such as those developed for recombinant antibodies

• Live-cell imaging approaches:

  • Develop fluorescent protein fusions that maintain DsbB functionality

  • Employ photoactivatable fluorescent proteins to track DsbB movement over time

  • Use FRAP (Fluorescence Recovery After Photobleaching) to measure DsbB mobility in the membrane

• Multi-color imaging:

  • Simultaneously visualize DsbB and interaction partners (DsbA, HmsC, HmsD)

  • Apply FRET (Förster Resonance Energy Transfer) to detect protein-protein interactions in living cells

  • Correlate spatial relationships with biofilm developmental stages

• Correlative microscopy:

  • Combine fluorescence imaging with electron microscopy to correlate DsbB localization with ultrastructural features

  • Implement cryo-electron tomography to visualize membrane protein complexes in near-native states

  • This approach can bridge molecular and cellular scales of observation

• Redox-sensitive probes:

  • Develop fluorescent sensors that report on local redox environments around DsbB

  • Create fusion constructs with redox-sensitive GFP variants

  • Map the spatiotemporal dynamics of redox changes during biofilm formation

These advanced imaging approaches would provide unprecedented insights into how DsbB functions within the complex three-dimensional architecture of Y. pestis biofilms, potentially revealing new targets for intervention strategies.

What genomic approaches could reveal the evolution of DsbB-dependent redox sensing in different Yersinia species?

Genomic approaches offer powerful tools to understand the evolution of DsbB-dependent redox sensing across Yersinia species and potentially identify adaptations specific to Y. pestis. Promising research directions include:

• Comparative genomics:

  • Analyze dsbB sequences and genetic contexts across all Yersinia species

  • Compare with related Enterobacteriaceae to identify Yersinia-specific features

  • Identify coevolving gene pairs (e.g., dsbB with hmsC/D/E) that suggest functional relationships

  • This approach could reveal how the DsbB-HmsCDE regulatory network evolved specifically in Y. pestis

• Population genomics:

  • Sequence dsbB from multiple clinical and environmental isolates of Y. pestis

  • Identify natural polymorphisms and their distribution across different lineages

  • Correlate genetic variations with biofilm formation phenotypes

  • Look for signatures of selection that might indicate adaptation to different hosts or vectors

• Transcriptomics:

  • Perform RNA-Seq on wild-type and dsbB mutant strains under various conditions

  • Identify genes differentially regulated in response to altered redox states

  • Map the complete redox-responsive regulon in Y. pestis

  • Compare transcriptional responses across Yersinia species to identify conserved versus species-specific responses

• Experimental evolution:

  • Subject Y. pestis to alternating selection for biofilm formation and planktonic growth

  • Sequence evolved strains to identify mutations affecting the DsbB pathway

  • This approach could reveal alternative evolutionary trajectories for redox sensing

• Ancestral sequence reconstruction:

  • Infer ancestral sequences of DsbB in Yersinia

  • Resurrect and characterize these proteins to understand functional evolution

  • Identify key mutations that altered DsbB function during the emergence of Y. pestis

These genomic approaches would provide a deeper understanding of how Y. pestis has evolved its specialized redox sensing system, potentially revealing how this pathogen adapted to its unique transmission cycle between fleas and mammals, and identifying vulnerabilities that could be exploited for therapeutic development.