Recombinant Haemophilus ducreyi UPF0283 membrane protein HD_1769 (HD_1769)

What is Haemophilus ducreyi UPF0283 membrane protein HD_1769?

Haemophilus ducreyi UPF0283 membrane protein HD_1769 is a membrane-associated protein found in Haemophilus ducreyi strain 35000HP / ATCC 700724. It is classified as part of the UPF0283 protein family, a group of proteins with conserved sequences but initially uncharacterized functions. The protein is encoded by the HD_1769 gene locus in the H. ducreyi genome and has a Uniprot accession number of P59917 .

The complete amino acid sequence consists of 341 amino acids, making it a medium-sized membrane protein. The primary sequence suggests a transmembrane structure with multiple hydrophobic regions that likely span the bacterial outer membrane, contributing to the organism's membrane integrity and potentially playing roles in pathogenesis or environmental adaptation .

What are the optimal expression systems for producing recombinant HD_1769 protein?

Successful expression of recombinant HD_1769 protein has been achieved using Escherichia coli expression systems, particularly those utilizing the T7 promoter system. Based on approaches used for similar H. ducreyi membrane proteins, the following methodology is recommended:

• Cloning strategy: Clone the HD_1769 gene without its leader sequence behind a T7-inducible promoter (similar to the strategy used for other H. ducreyi outer membrane proteins) .

• Expression vectors: pET30a plasmid systems with hexahistidine tag fusion have proven effective for expressing similar H. ducreyi membrane proteins .

• Host strains: E. coli BL21(DE3) pLysS or Nova Blue (DE3) are suitable host strains for expressing H. ducreyi membrane proteins .

• Induction protocol: Culture to mid-log phase (OD600 of 0.5), induce with IPTG (2 mM), and add rifampin (200 μg/ml) after 30 minutes to inhibit host RNA polymerase and enhance recombinant protein expression .

This system typically leads to the formation of inclusion bodies containing high concentrations of the recombinant protein, which can be isolated and purified under appropriate conditions.

What are the recommended storage conditions for recombinant HD_1769 protein?

For optimal stability and activity of recombinant HD_1769 protein, the following storage conditions are recommended:

• Short-term storage (up to one week): Store working aliquots at 4°C in Tris-based buffer with 50% glycerol that has been optimized for this specific protein .

• Medium-term storage: Store at -20°C in single-use aliquots to avoid repeated freeze-thaw cycles .

• Long-term storage: For extended preservation, store at -80°C in small aliquots (50-100 μL) to minimize freeze-thaw damage .

The addition of protease inhibitors to the storage buffer may help prevent degradation, particularly for research applications requiring preserved structural integrity of the protein.

What purification methods yield the highest purity of recombinant HD_1769 protein?

Achieving high purity recombinant HD_1769 protein requires a multi-step purification protocol that addresses the challenges associated with membrane proteins:

• Inclusion body isolation: After cell lysis using a French press or sonication, centrifuge at 10,000 × g to isolate inclusion bodies containing the recombinant protein .

• Solubilization: Solubilize inclusion bodies using denaturing conditions (typically 6-8 M urea or 6 M guanidine hydrochloride) .

• Metal chelate chromatography: Purify the His-tagged recombinant protein using Ni-NTA or similar metal chelate chromatography under denaturing conditions .

• Refolding: Perform gradual dialysis to remove denaturants and allow proper refolding of the protein structure.

• Additional purification: If necessary, employ size exclusion chromatography or ion exchange chromatography to remove truncated products or contaminants.

When evaluating purification quality, SDS-PAGE analysis typically reveals potential challenges with recombinant HD_1769 protein, including the presence of smaller immunoreactive bands that are not E. coli contaminants but likely truncated forms of the recombinant protein . These fragments may result from either premature translation termination or proteolytic degradation during expression or purification.

How can recombinant HD_1769 protein be used in diagnostic assays for H. ducreyi infection?

The recombinant HD_1769 protein has potential applications in serological diagnostic assays for H. ducreyi infection. Based on approaches used with other H. ducreyi membrane proteins, researchers can develop diagnostic methods following these guidelines:

• Enzyme immunoassay (EIA) development:

  • Coat microtiter plates with purified recombinant HD_1769 protein

  • Challenge with patient sera at appropriate dilutions

  • Detect human antibodies using enzyme-conjugated anti-human immunoglobulin

  • Establish cutoff values using sera from patients with confirmed H. ducreyi infection and from healthy controls

• Optimization parameters:

  • Concentration of coating antigen (typically 1-10 μg/ml)

  • Serum dilution (typically 1:100 to 1:500)

  • Incubation times and temperatures

  • Blocking agents to minimize non-specific binding

• Performance evaluation:

  • Determine sensitivity and specificity using panels of characterized sera

  • Evaluate cross-reactivity with antibodies against other Haemophilus species

  • Assess potential interference from concomitant infections

It should be noted that serological tests for H. ducreyi have limitations, including delayed antibody responses, cross-reactivity issues, and persistent antibodies after infection clearance . Therefore, complementary testing methods may be necessary for comprehensive diagnosis.

What methodological approaches can be used to study HD_1769 protein interactions with host immune cells?

Investigating interactions between HD_1769 protein and host immune cells requires multiple complementary methodological approaches:

• Binding assays:

  • Flow cytometry to quantify binding of fluorescently labeled recombinant HD_1769 to different immune cell populations

  • Surface plasmon resonance (SPR) to determine binding kinetics and affinity for specific immune receptors

  • Microscopy-based approaches to visualize protein localization during host-pathogen interactions

• Functional assays:

  • Cytokine production measurement following stimulation of immune cells with recombinant HD_1769

  • Analysis of signal transduction pathway activation using phospho-specific antibodies

  • Gene expression profiling of immune cells after exposure to the protein

• In vitro cell culture models:

  • Co-culture systems combining recombinant HD_1769 with human skin immune cells

  • Three-dimensional skin models to study protein interactions in a tissue context

  • Gentamicin protection assays to evaluate the impact on intracellular survival

• Structural biology approaches:

  • Epitope mapping to identify immunologically relevant regions of HD_1769

  • Protein-protein interaction studies using crosslinking followed by mass spectrometry

  • Structural determination through X-ray crystallography or cryo-electron microscopy

When designing these experiments, researchers should consider the native conformation of the protein, as denatured recombinant proteins may not accurately represent physiological interactions. Additionally, complementary experiments using isogenic mutant strains of H. ducreyi lacking HD_1769 can provide validation of in vitro findings using recombinant protein.

What bioinformatic tools and approaches can help predict the structure and function of HD_1769 protein?

Comprehensive bioinformatic analysis of HD_1769 protein can provide valuable insights into its structure and potential functions:

• Sequence analysis tools:

  • Multiple sequence alignment with homologous proteins using CLUSTAL Omega or MUSCLE

  • Identification of conserved domains using InterPro, PFAM, or CDD databases

  • Analysis of amino acid composition and physico-chemical properties using ProtParam

• Structural prediction:

  • Secondary structure prediction using PSIPRED or JPred

  • Tertiary structure modeling using AlphaFold2, I-TASSER, or SWISS-MODEL

  • Membrane topology prediction using TMHMM, TOPCONS, or Phobius

• Functional annotation:

  • Gene Ontology (GO) term assignment

  • Protein-protein interaction prediction using STRING database

  • Functional site prediction using ConSurf or 3DLigandSite

• Evolutionary analysis:

  • Phylogenetic tree construction to understand evolutionary relationships

  • Identification of orthologs in related bacterial species

  • Selection pressure analysis to identify functionally important residues

Based on the amino acid sequence provided in search result , initial analysis suggests multiple hydrophobic regions consistent with a transmembrane protein, and the presence of specific sequence motifs may indicate potential roles in membrane transport or signaling.

How does HD_1769 compare to other well-characterized membrane proteins of H. ducreyi?

Comparative analysis of HD_1769 with other characterized H. ducreyi membrane proteins reveals important distinctions in structure, function, and immunological properties:

• Size and structure comparison:
  The 341-amino acid HD_1769 protein differs from other key H. ducreyi membrane proteins such as:

  • HgbA (hemoglobin receptor): Significantly larger (approximately 100 kDa)

  • TdhA (heme receptor): Different topology and binding sites

  • D15: Different structural organization despite similar membrane localization

• Expression patterns:
  Unlike some H. ducreyi proteins that show variable expression under different environmental conditions, HD_1769 appears to be constitutively expressed, suggesting a fundamental role in membrane structure or function.

• Immunological properties:
  While HgbA, TdhA, and D15 have been shown to be highly immunogenic during natural infection and have been successfully used in serological assays , the immunogenicity of HD_1769 requires further investigation.

• Known functions:
  Unlike HgbA and TdhA, which have defined roles in hemoglobin and heme acquisition respectively , the specific function of HD_1769 remains to be fully characterized. Its classification as a UPF0283 family member indicates a conserved but initially uncharacterized function.

These comparative insights can guide experimental approaches for characterizing HD_1769 and help researchers leverage knowledge from better-understood H. ducreyi proteins.

What are the optimal protocols for producing polyclonal or monoclonal antibodies against HD_1769 protein?

Developing specific antibodies against HD_1769 requires careful consideration of antigen preparation and immunization protocols:

• Polyclonal antibody production:

  • Antigen preparation: Use purified recombinant HD_1769 protein or synthetic peptides corresponding to predicted immunogenic epitopes (preferably extracellular domains)

  • Animal selection: Rabbits are recommended for generating polyclonal antibodies against H. ducreyi proteins

  • Immunization protocol: Primary immunization with complete Freund's adjuvant followed by 3-4 booster injections with incomplete Freund's adjuvant at 2-3 week intervals

  • Antibody purification: Affinity purification against the immunizing antigen to reduce non-specific binding

• Monoclonal antibody production:

  • Immunization: Similar to polyclonal protocol but using mice or rats

  • Hybridoma generation: Standard fusion protocol with screening for HD_1769-specific antibodies

  • Clone selection: Screen for antibodies that recognize native conformation of the protein

  • Production and purification: Scale up selected hybridomas and purify antibodies using protein A/G

• Antibody validation:

  • Western blotting against recombinant HD_1769 and H. ducreyi lysates

  • Immunoprecipitation to confirm specificity

  • Immunofluorescence microscopy to verify recognition of the native protein in intact bacteria

  • Functional assays to determine if antibodies block potential functions of the protein

When designing synthetic peptide antigens for antibody production, researchers should analyze the HD_1769 sequence for regions likely to be exposed to the immune system and with high predicted antigenicity. Based on the amino acid sequence provided , regions with hydrophilic profiles and predicted B-cell epitopes would make promising candidates for peptide synthesis.

What experimental approaches can elucidate the role of HD_1769 in H. ducreyi pathogenesis?

A comprehensive investigation of HD_1769's role in pathogenesis requires multiple experimental approaches:

• Genetic manipulation strategies:

  • Construction of isogenic knockout mutants using allelic exchange

  • Complementation studies to confirm phenotypes

  • Creation of reporter fusions to study expression patterns during infection

• In vitro infection models:

  • Human keratinocyte adhesion and invasion assays

  • Macrophage and neutrophil interaction studies

  • Biofilm formation assays comparing wild-type and mutant strains

• Ex vivo tissue models:

  • Human skin explant infection model to assess tissue damage and bacterial localization

  • Three-dimensional reconstructed human epidermis model to study bacterial-epithelial interactions

  • Microfluidic organ-on-chip approaches to simulate dynamic host-pathogen interactions

• In vivo studies:

  • Human challenge model comparing wild-type and HD_1769 mutant strains

  • Assessment of bacterial colonization, ulcer formation, and immune response

• Functional characterization:

  • Membrane integrity assays to assess potential structural roles

  • Transport assays if HD_1769 is hypothesized to function in nutrient acquisition

  • Resistance to host defense mechanisms (antimicrobial peptides, complement)

Given the laboratory challenges in working with H. ducreyi, including its fastidious growth requirements and rapid loss of viability outside the human host , these experiments require careful optimization of culture conditions and rapid processing of samples.

How can potential post-translational modifications of HD_1769 be identified and characterized?

Identifying and characterizing post-translational modifications (PTMs) of HD_1769 requires specialized techniques:

• Mass spectrometry-based approaches:

  • Sample preparation: Purify native HD_1769 from H. ducreyi cultures or express recombinant protein in systems that perform relevant PTMs

  • Proteolytic digestion: Use multiple proteases (trypsin, chymotrypsin, Glu-C) to ensure comprehensive sequence coverage

  • Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis with data-dependent acquisition

  • Targeted analysis for specific modifications using multiple reaction monitoring (MRM)

• Modification-specific detection methods:

  • Glycosylation: Periodic acid-Schiff (PAS) staining, lectin blotting, or glycoprotein-specific staining

  • Phosphorylation: Western blotting with phospho-specific antibodies, Phos-tag SDS-PAGE

  • Lipidation: Metabolic labeling with radioactive or clickable lipid precursors

• Site-directed mutagenesis:

  • Mutate potential modification sites and assess functional consequences

  • Create modification-mimicking mutations (e.g., Ser/Thr to Asp/Glu for phosphorylation)

  • Evaluate the impact on protein localization, stability, and function

• Structural analysis:

  • X-ray crystallography or cryo-EM to visualize modifications in the context of protein structure

  • NMR spectroscopy for dynamic analysis of modification effects

For membrane proteins like HD_1769, common bacterial post-translational modifications to investigate include lipidation (particularly N-terminal lipidation common in bacterial membrane proteins), phosphorylation, and glycosylation. The UPF0283 protein family may have characteristic modifications that could provide clues to function.

What are the challenges and solutions in crystallizing HD_1769 for structural studies?

Membrane proteins like HD_1769 present significant challenges for crystallization and structural determination:

• Key challenges:

  • Hydrophobicity and insolubility in aqueous solutions

  • Conformational heterogeneity

  • Difficulty in obtaining sufficient quantities of properly folded protein

  • Presence of flexible regions that may impede crystal formation

• Production strategies:

  • Expression of truncated constructs lacking flexible regions

  • Fusion with crystallization chaperones (e.g., T4 lysozyme, BRIL)

  • Co-expression with stabilizing partner proteins

  • Expression in specialized membrane protein expression systems

• Solubilization and stabilization approaches:

  • Screening of detergents for optimal extraction and stability

  • Use of lipid cubic phase (LCP) for membrane protein crystallization

  • Amphipol or nanodisc reconstitution for native-like membrane environment

  • Thermostabilizing mutations to reduce conformational heterogeneity

• Crystallization optimization:

  • High-throughput crystallization screening

  • Optimization of protein-to-detergent ratio

  • Addition of specific ligands or antibody fragments to stabilize conformation

  • Utilization of specialized crystallization methods (LCP, bicelles, vapor diffusion)

• Alternative structural approaches:

  • Cryo-electron microscopy for structure determination without crystals

  • NMR spectroscopy for dynamic structural information

  • Small-angle X-ray scattering (SAXS) for low-resolution envelope determination

Based on the sequence information for HD_1769 , bioinformatic analysis can predict potential flexible regions that might hinder crystallization, guiding the design of constructs with higher crystallization propensity.

What are the current limitations in HD_1769 research and potential strategies to overcome them?

Current research on HD_1769 faces several significant limitations that require innovative solutions:

• Knowledge gaps:

  • Limited functional characterization compared to other H. ducreyi membrane proteins

  • Uncertainty about natural ligands or binding partners

  • Incomplete understanding of regulation and expression patterns during infection

• Technical challenges:

  • Difficulty in culturing H. ducreyi due to its fastidious nature

  • Limited genetic manipulation tools compared to model organisms

  • Challenges in structural studies of membrane proteins

• Methodological strategies to overcome limitations:

  • Development of improved genetic tools for H. ducreyi manipulation

  • Application of systems biology approaches (transcriptomics, proteomics)

  • Adaptation of single-cell techniques to study heterogeneity

  • Cross-disciplinary approaches combining structural biology, genetics, and immunology

• Collaborative approaches:

  • Integration of clinical and basic research

  • Partnerships between laboratories with complementary expertise

  • Development of standardized protocols and reagent sharing

Future research directions should focus on characterizing the function of HD_1769 in the context of H. ducreyi pathogenesis, potentially revealing new therapeutic targets for chancroid and cutaneous ulcer treatment.

How can conflicting experimental data about HD_1769 function be reconciled and validated?

When facing conflicting experimental results regarding HD_1769 function, researchers should consider:

• Systematic validation approaches:

  • Independent replication in different laboratories

  • Utilization of multiple complementary techniques to address the same question

  • Careful evaluation of experimental conditions that might explain discrepancies

• Common sources of experimental discrepancies:

  • Different expression systems affecting protein folding or modifications

  • Variations in purification methods leading to different conformational states

  • Host cell type differences in interaction studies

  • Strain-specific variations in bacterial studies

• Reconciliation strategies:

  • Meta-analysis of available data to identify patterns and outliers

  • Development of standardized assay conditions and reporting formats

  • Side-by-side comparison of conflicting protocols to identify critical variables

• Advanced validation techniques:

  • In vivo validation of in vitro findings

  • Correlation of functional data with structural information

  • Integration of computational models with experimental results

By systematically addressing potential sources of variability and employing rigorous validation, researchers can develop a more coherent understanding of HD_1769 function despite initial conflicting results.

How can CRISPR-Cas9 technology be applied to study HD_1769 function in H. ducreyi?

CRISPR-Cas9 technology offers powerful approaches for studying HD_1769 function:

• Genetic manipulation strategies:

  • Targeted gene knockout with minimal polar effects

  • Precise introduction of point mutations to study specific protein domains

  • Creation of regulated expression systems through promoter modifications

  • Tagging of endogenous HD_1769 with reporters for localization studies

• Technical considerations for H. ducreyi:

  • Optimization of transformation protocols for efficient delivery

  • Selection of appropriate Cas9 variants and guide RNA design

  • Development of tailored homology-directed repair templates

  • Screening methods for identifying successful genome edits

• Advanced applications:

  • CRISPRi for inducible gene repression to study essential genes

  • CRISPRa for upregulation to assess overexpression phenotypes

  • Multiplexed editing to study potential functional redundancy

  • CRISPR-based imaging for tracking protein dynamics

• Validation requirements:

  • Confirmation of genomic modifications by sequencing

  • Analysis of off-target effects

  • Complementation studies to verify specificity of phenotypes

  • Careful controls for CRISPR system effects

Researchers implementing CRISPR-Cas9 approaches for studying HD_1769 should be aware that optimization will likely be required for the specific characteristics of H. ducreyi, as the efficiency of CRISPR systems can vary between bacterial species.

What high-throughput screening approaches can identify small molecule modulators of HD_1769 function?

Identifying small molecule modulators of HD_1769 function requires systematic screening approaches:

• Assay development strategies:

  • Functional assays based on predicted activities (e.g., transport, binding)

  • Reporter systems linked to HD_1769 activity or expression

  • Growth or survival assays in HD_1769-dependent conditions

  • Binding assays using purified recombinant protein

• Compound library selection:

  • Focused libraries based on predicted binding sites or function

  • Natural product collections with historical activity against bacteria

  • Fragment-based approaches for initial hit identification

  • Repurposing libraries of clinically tested compounds

• Screening methodologies:

  • Primary high-throughput screening at single concentration

  • Dose-response confirmation of primary hits

  • Counter-screening against related proteins to assess specificity

  • Mechanism of action studies for promising candidates

• Hit validation and optimization:

  • Structure-activity relationship studies

  • Target engagement confirmation (thermal shift assays, cellular target engagement)

  • Resistance development studies

  • Medicinal chemistry optimization of promising scaffolds

For membrane proteins like HD_1769, developing assays that maintain the native conformation and environment of the protein presents a particular challenge. Approaches such as whole-cell screening or reconstitution in artificial membrane systems may provide more physiologically relevant conditions than assays using purified protein in detergent solutions.

By systematically applying these approaches, researchers may identify tool compounds that can help elucidate HD_1769 function or potentially lead to new therapeutic strategies targeting H. ducreyi.