Recombinant Pasteurella multocida UPF0208 membrane protein PM0703 (PM0703)

What is Pasteurella multocida UPF0208 membrane protein PM0703?

[BASIC] PM0703 is a membrane protein from Pasteurella multocida (strain Pm70) belonging to the UPF0208 protein family. The protein consists of 147 amino acids with the sequence: MYFFIFLKKGQHYLKSWPLESKLGMIFPENRVIKATLFAQKFMPFLAVFAITWQQVYAKSDISALAIAVFSAIVALLIPLQGLYWLGKRSITPLSPQSAVWFYEICERLKQVNETLPILTEQPNYQNLADVLKKAQRKLDKAFWQEL. It is encoded by the PM0703 gene locus and represents a full-length protein with potential roles in membrane integrity and cellular functions .

The protein contains hydrophobic regions typical of membrane proteins, with alternating hydrophobic and hydrophilic segments that facilitate anchoring in the bacterial membrane. While its specific function is not fully characterized, it shares structural similarities with other bacterial membrane proteins involved in maintaining membrane integrity and potentially in host-pathogen interactions.

How does PM0703 compare structurally to other characterized membrane proteins of P. multocida?

[ADVANCED] PM0703 shows distinct structural differences when compared to other well-characterized membrane proteins of P. multocida such as OmpA, OmpH, and PlpE. Unlike OmpH, which is a porin protein detected in 100% of bovine isolates and has been investigated as a potential vaccine candidate, PM0703 has a smaller molecular weight and lacks the β-barrel structure typical of porins .

While OmpA proteins typically function as adhesins that bind host cells and extracellular matrix molecules, PM0703 lacks the conserved domains associated with this function . PlpE, another immunogenic outer membrane protein of P. multocida that has shown protective efficacy in vaccination studies, contains specific epitopes that elicit protective immune responses, a characteristic not yet established for PM0703 .

The structural analysis suggests PM0703's role may be more related to basic membrane integrity rather than the specific host-pathogen interaction functions demonstrated by OmpH and PlpE proteins.

What expression systems are most effective for recombinant production of PM0703?

[BASIC] E. coli-based expression systems are most commonly used for the recombinant production of PM0703, similar to other P. multocida membrane proteins. Based on methodologies used for similar proteins, the following approach is recommended:

• Cloning strategy: The PM0703 gene should be PCR-amplified using specific primers with appropriate restriction sites (typically BamHI and BglII) to facilitate directional cloning .

• Vector selection: For initial cloning, pGEMT Easy vector can be used, followed by subcloning into an expression vector such as pET28a(+) that provides an N-terminal His-tag for purification purposes .

• Expression host: E. coli BL21(DE3) is the preferred host strain due to its deficiency in lon and ompT proteases, which helps in preserving the recombinant protein integrity.

• Induction conditions: Optimal expression is typically achieved with 0.5-1.0 mM IPTG induction at 28°C for 4-6 hours, as higher temperatures may lead to inclusion body formation with membrane proteins.

This methodology has been successfully applied to other P. multocida membrane proteins and should be adaptable for PM0703 with minor optimizations based on protein-specific characteristics.

What purification challenges are specific to PM0703, and how can they be addressed?

[ADVANCED] Purification of recombinant PM0703 presents several challenges common to membrane proteins, including low solubility, potential toxicity to expression hosts, and proper refolding. Based on experiences with similar membrane proteins from P. multocida, the following methodological approach is recommended:

• Solubilization strategy: Use mild detergents like n-dodecyl-β-D-maltoside (DDM) or CHAPS at concentrations just above their critical micelle concentration to extract PM0703 from membranes without denaturing its structure.

• Two-phase purification protocol:

  • Initial capture using immobilized metal affinity chromatography (IMAC) with Ni-NTA resin for His-tagged protein

  • Secondary purification using size exclusion chromatography to remove aggregates and impurities

• Refolding considerations: If inclusion bodies form, employ a gradual dialysis method with decreasing concentrations of urea (8M to 0M) in the presence of appropriate detergents to facilitate proper refolding.

• Storage optimization: The purified protein should be stored in a Tris-based buffer with 50% glycerol at -20°C, with working aliquots kept at 4°C for up to one week to prevent protein degradation from repeated freeze-thaw cycles .

Verification of proper folding can be achieved through circular dichroism spectroscopy to confirm secondary structure elements expected in membrane proteins.

What functional assays can determine the biological activity of recombinant PM0703?

[ADVANCED] Several functional assays can be employed to characterize the biological activity of recombinant PM0703:

• Membrane integration assays: Liposome incorporation studies can determine if recombinant PM0703 properly integrates into lipid bilayers, which is essential for its native function.

• Ion channel activity assessment: Planar lipid bilayer electrophysiology can determine if PM0703 forms channels or pores, measuring conductance changes under various voltage conditions.

• Protein-protein interaction studies:

  • Pull-down assays with potential interaction partners

  • Bacterial two-hybrid systems to identify protein complexes in vivo

  • Surface plasmon resonance to measure binding kinetics with host proteins

• Adhesion and invasion assays: Using cell culture models to assess if PM0703 mediates bacterial adhesion to host cells, similar to other membrane proteins like OmpA that function as adhesins binding host cells and extracellular matrix molecules .

• Immunogenicity assessment: ELISA and Western blot analysis using sera from infected animals to determine if PM0703 is recognized by the immune system during natural infection, as has been established for OmpH and PlpE proteins .

These functional analyses would provide insights into PM0703's role in bacterial physiology and host-pathogen interactions.

How can PM0703 be evaluated for potential vaccine development?

[ADVANCED] Evaluation of PM0703 as a vaccine candidate should follow a systematic approach based on methodologies used for other P. multocida membrane proteins:

• Immunogenicity assessment:

  • Measure antibody responses (IgG, IgA) in mice immunized with purified recombinant PM0703

  • Analyze isotype distribution (IgG1 vs. IgG2a) to determine Th1/Th2 bias of immune response

  • Quantify cytokine production (IFN-γ, IL-4) from stimulated splenocytes to assess cell-mediated immunity

• Protection studies in animal models:

  • Immunize mice with different formulations of recombinant PM0703

  • Challenge with virulent P. multocida strains

  • Monitor survival rates, bacterial loads in tissues, and clinical signs

• Adjuvant optimization:

  • Test various adjuvant combinations (e.g., Montanide modified-CpG ODN, which has shown success with other P. multocida proteins)

  • Evaluate route of administration (subcutaneous, intraperitoneal, intranasal)

When evaluating PM0703 as a vaccine candidate, it's important to consider the potential outcomes observed with other membrane proteins. For instance, unlike PlpE which conferred 100% protection in mice when administered with appropriate adjuvants, OmpA has been found to elicit a Th2-type immune response characterized by high IgG1 antibody production but failed to provide protection against challenge infection . This highlights the importance of carefully assessing the type of immune response elicited by PM0703.

How does the immunogenicity of PM0703 compare with other P. multocida membrane proteins?

[ADVANCED] While specific immunogenicity data for PM0703 is limited, comparative analysis with other P. multocida membrane proteins provides a framework for understanding its potential immunological properties:

Based on trends observed with other membrane proteins, several factors could influence PM0703's immunogenicity:

• Structural accessibility of epitopes on the bacterial surface

• Conservation across different P. multocida serotypes

• Ability to induce balanced Th1/Th2 responses rather than skewed responses

• Potential synergistic or antagonistic effects when combined with other antigens

Research suggests that for membrane proteins like OmpH, native conformation is critical for protective immunity, with recombinant versions showing reduced efficacy compared to native forms . This emphasizes the importance of proper folding in recombinant PM0703 production for immunological studies.

What evolutionary conservation patterns are observed for PM0703 across Pasteurella species?

[BASIC] Evolutionary conservation analysis of PM0703 can provide insights into its functional importance and potential as a broadly protective antigen. While specific phylogenetic data for PM0703 is not provided in the search results, methodological approaches can be derived from studies on other P. multocida proteins:

• Sequence alignment analysis:

  • Multiple sequence alignment of PM0703 homologs across Pasteurella species and strains

  • Identification of conserved motifs and variable regions

  • Calculation of sequence identity percentages between homologs

• Phylogenetic tree construction:

  • Using maximum likelihood or neighbor-joining methods

  • Bootstrap analysis to determine confidence in tree topology

  • Correlation with serotype distribution and host specificity

Based on studies of other P. multocida proteins, such as the kmt1 gene which showed remarkable genetic identity across strains from the USA, Denmark, China, India, and Iran , membrane proteins often display varying degrees of conservation. Highly conserved regions may indicate functional importance, while variable regions might be involved in serotype-specific interactions or immune evasion.

How can PM0703 be used to study P. multocida virulence mechanisms?

[ADVANCED] PM0703 can serve as a valuable tool for investigating P. multocida virulence mechanisms through several experimental approaches:

• Gene knockout studies:

  • Creating PM0703 deletion mutants using homologous recombination or CRISPR-Cas systems

  • Assessing changes in bacterial fitness, membrane integrity, and virulence

  • In vitro and in vivo infection models to determine contribution to pathogenesis

• Protein localization and expression studies:

  • Immunofluorescence microscopy to determine subcellular localization during infection

  • qRT-PCR and Western blot analysis to assess expression under different environmental conditions

  • Promoter fusion studies to identify regulatory mechanisms controlling expression

• Host-pathogen interaction studies:

  • Pull-down assays to identify host proteins that interact with PM0703

  • Cell signaling analysis to determine effects on host cell pathways

  • Assessment of PM0703's role in immune evasion strategies

When designing these studies, researchers should consider the known virulence factors of P. multocida identified across different strains. Recent research has shown that virulence genes such as oma87, ptfA, luxS, tadG, and nanB have prevalence rates of 100%, 86.7%, 76.6%, 73.3%, and 56.7%, respectively, highlighting the complex virulence profile of this pathogen . Understanding where PM0703 fits within this virulence network would provide valuable insights into P. multocida pathogenesis.

What methodologies are most effective for monitoring PM0703 expression during infection?

[BASIC] Monitoring PM0703 expression during infection requires sensitive and specific methodologies that can detect protein or transcript levels in complex biological samples:

• Transcript-level analysis:

  • qRT-PCR using primers specific to the PM0703 gene

  • RNA-Seq for genome-wide expression profiling, including PM0703

  • In situ hybridization to visualize transcript localization in infected tissues

• Protein-level analysis:

  • Western blot with specific antibodies against recombinant PM0703

  • Immunohistochemistry to visualize protein expression in infected tissues

  • ELISA assays for quantitative measurement in tissue homogenates

  • Mass spectrometry-based proteomics for unbiased detection

• Reporter systems:

  • Construction of PM0703 promoter-reporter fusions (GFP, luciferase)

  • In vivo imaging of reporter activity during infection progression

  • Flow cytometry to quantify expression at the single-cell level

A comprehensive approach would combine these methodologies to correlate PM0703 expression with different stages of infection and in response to various host environments. This would provide insights into the potential role of PM0703 in adaptation to host niches and its contribution to virulence.

What are common challenges in obtaining soluble recombinant PM0703, and how can they be addressed?

[BASIC] Membrane proteins like PM0703 present several common challenges during recombinant expression and purification. The following methodological solutions can help overcome these issues:

• Inclusion body formation:

  • Reduce expression temperature to 16-20°C

  • Use weaker promoters to slow expression rate

  • Co-express with molecular chaperones (GroEL/GroES, DnaK/DnaJ)

  • Optimize media composition with osmolytes like sorbitol or glycine betaine

• Low expression yields:

  • Use codon-optimized gene sequences for expression host

  • Test different fusion tags (MBP, SUMO, TrxA) that enhance solubility

  • Screen multiple E. coli strains (C41/C43, SHuffle, Origami)

  • Consider cell-free expression systems for toxic proteins

• Protein instability:

  • Include protease inhibitors throughout purification

  • Store in stabilizing buffer with 50% glycerol as recommended for PM0703

  • Add specific lipids to mimic native membrane environment

  • Avoid repeated freeze-thaw cycles by storing working aliquots at 4°C for short-term use

• Verification of proper folding:

  • Circular dichroism to assess secondary structure

  • Thermal shift assays to evaluate stability

  • Limited proteolysis to probe tertiary structure

Following these approaches has proven effective for other challenging membrane proteins and should be adaptable for PM0703 expression and purification.

How can researchers optimize experimental design when studying potential immunological properties of PM0703?

[ADVANCED] When investigating the immunological properties of PM0703, researchers should consider several methodological optimizations based on lessons learned from other P. multocida membrane proteins:

• Antigen preparation considerations:

  • Ensure native-like conformation of recombinant PM0703

  • Remove endotoxin contamination (< 0.1 EU/μg protein)

  • Quantify protein accurately using multiple methods (BCA, Bradford)

  • Verify structural integrity before immunization studies

• Immunization protocol design:

  • Test multiple adjuvant formulations (Freund's, Montanide, CpG ODN)

  • Compare different routes of administration (subcutaneous, intraperitoneal, intranasal)

  • Include appropriate controls (adjuvant only, irrelevant protein)

  • Collect samples at multiple timepoints to track response kinetics

• Immune response evaluation:

  • Assess both humoral (antibody) and cellular (T cell) responses

  • Determine antibody isotype distribution (IgG1/IgG2a ratio) to characterize Th1/Th2 bias

  • Measure cytokine profiles from restimulated splenocytes

  • Evaluate functional antibody properties (opsonization, neutralization)

• Challenge study design:

  • Use clinically relevant challenge strains

  • Determine appropriate challenge dose through pilot studies

  • Monitor multiple outcomes (survival, bacterial load, clinical scores)

  • Perform adequate power analysis to determine group sizes

It's important to note that the immune response to membrane proteins can vary significantly. For example, while OmpH showed protective efficacy when properly formulated, OmpA elicited a strong Th2-type immune response with high IgG1 antibodies but failed to provide protection . This demonstrates that a strong antibody response alone doesn't guarantee protection, and the type of immune response is critical.