Recombinant Haemophilus influenzae Uncharacterized aquaporin-like protein HI_1017 (HI_1017)

What is the primary structure of the HI_1017 protein?

HI_1017 is a full-length protein consisting of 213 amino acids. Its complete amino acid sequence is: MCQYFLKKIRNVWERWFTYRLWFGLSMVSIAVIFGPLTGAHVNPAVTIDFWEVGKFPTELVLVYIIAQCIGAFIVALIVWLLFKDHLDEEDNQNCQLGSFATIATNSNNLRNLLSEIVTTFSLLFILFTLNHQQPTNGVAMFFVFTGVAGGVMSFGGLTSYAINPARDFMLRLIHAIMPIKNKGTSNFDYAWVPVLRPVIGAILAAWLYKALF . Analysis of this sequence reveals characteristic transmembrane domains typical of aquaporin family proteins, suggesting a potential role in selective membrane transport. Researchers should begin characterization by conducting hydropathy plot analysis and identifying conserved NPA (Asparagine-Proline-Alanine) motifs that are hallmarks of aquaporin channel proteins.

How is recombinant HI_1017 typically produced for research purposes?

Recombinant HI_1017 is commonly expressed in E. coli expression systems with an N-terminal histidine tag to facilitate purification . The gene encoding the full-length protein (amino acids 1-213) is cloned into an appropriate expression vector, transformed into E. coli, and protein expression is typically induced under controlled conditions. After cell lysis, the His-tagged protein is purified using affinity chromatography, commonly with Ni-NTA resin. The purified protein is then typically lyophilized as a powder for storage stability . For reconstitution, researchers should use deionized sterile water to achieve concentrations of 0.1-1.0 mg/mL, with the addition of 5-50% glycerol (final concentration) recommended for long-term storage at -20°C/-80°C .

What storage conditions are optimal for maintaining HI_1017 stability?

Lyophilized HI_1017 should be stored at -20°C/-80°C upon receipt . After reconstitution, the protein should be aliquoted to avoid repeated freeze-thaw cycles, which can significantly compromise protein integrity and functionality . Working aliquots can be stored at 4°C for up to one week . The recommended storage buffer is Tris/PBS-based buffer containing 6% Trehalose at pH 8.0 . Alternative storage formulations include Tris-based buffer with 50% glycerol, which has been optimized for this specific protein . Before use, vials should be briefly centrifuged to ensure all content is at the bottom of the tube.

What methodologies are recommended for determining the tertiary structure of HI_1017?

For structural characterization of HI_1017, a multi-technique approach is recommended. X-ray crystallography remains the gold standard, requiring the production of highly pure, homogeneous protein samples. For membrane proteins like HI_1017, crystallization in lipidic cubic phases has proven effective for related aquaporins. Alternatively, cryo-electron microscopy (cryo-EM) offers advantages for membrane proteins without requiring crystallization. Nuclear Magnetic Resonance (NMR) spectroscopy can provide valuable information about dynamics and ligand interactions if isotopically labeled protein can be produced. Computational approaches including homology modeling based on characterized aquaporins (such as AQP1) can provide preliminary structural insights before experimental determination. Circular dichroism spectroscopy should be used to assess secondary structure content and thermal stability.

How can researchers investigate the membrane topology of HI_1017?

To determine the membrane topology of HI_1017, researchers should employ a combination of experimental approaches. Protease protection assays using reconstituted protein in liposomes can identify exposed regions. Site-directed fluorescence labeling at predicted loop regions, combined with quenching experiments, can map transmembrane domain organization. Cysteine scanning mutagenesis with subsequent accessibility assays provides detailed information about water-accessible regions. Advanced approaches include Förster resonance energy transfer (FRET) experiments between strategically placed fluorophores to measure intramolecular distances. Given that aquaporins typically have six transmembrane domains with intracellular N- and C-termini, researchers should test whether HI_1017 conforms to this pattern or represents a structural variant.

What structural features distinguish HI_1017 from characterized aquaporins?

While HI_1017 is classified as an aquaporin-like protein, its sequence analysis reveals several unique features compared to well-characterized aquaporins. Sequence alignment with canonical aquaporins should focus on identifying conserved versus divergent regions, particularly examining the presence and positioning of NPA motifs that form the water-selective pore. Analysis of charged residues lining the putative channel can indicate selectivity differences. The presence of a longer N-terminal domain suggests potential regulatory functions not observed in conventional aquaporins. Researchers should investigate these distinctive features through targeted mutagenesis studies coupled with functional assays to determine their contribution to protein function and specificity.

What experimental systems can be used to characterize the transport properties of HI_1017?

To characterize transport function of HI_1017, researchers should employ proteoliposome-based systems where purified recombinant protein is reconstituted into artificial lipid vesicles. Water transport can be measured using stopped-flow spectroscopy with osmotic gradients, monitoring light scattering changes as vesicles shrink or swell. Alternative substrates should be systematically tested, including glycerol, ions, and small uncharged molecules, to determine if HI_1017 functions as a pure water channel or exhibits broader permeability. Electrophysiological measurements using planar lipid bilayers can detect ion conductance. For cellular studies, expression in Xenopus oocytes provides a well-established system for measuring membrane permeability through volume change assays or radioactive tracer uptake experiments.

How does the calcium signaling pathway potentially interact with aquaporin-like proteins?

Research on canonical aquaporins, particularly AQP1, has demonstrated that calcium signaling can regulate aquaporin function and expression. Evidence indicates that hypoxia inducible factor (HIF) activation increases intracellular calcium concentration ([Ca²⁺]ᵢ) in pulmonary arterial smooth muscle cells (PASMCs), which subsequently leads to increased AQP1 protein expression . This regulation occurs through calcium-dependent mechanisms rather than direct transcriptional regulation. For HI_1017, researchers should investigate whether calcium-dependent pathways modulate its expression or function through calcium channel blockers like verapamil or SKF96365 when studying the protein in cellular contexts . Fluorescence-based calcium imaging combined with HI_1017 expression analysis can help determine if similar regulatory mechanisms exist in bacterial systems.

What approaches can determine the physiological role of HI_1017 in Haemophilus influenzae?

To elucidate the physiological role of HI_1017 in H. influenzae, gene knockout studies represent the primary approach. CRISPR-Cas9 or homologous recombination techniques can generate HI_1017 deletion mutants. These mutants should be phenotypically characterized under various conditions, including osmotic stress, desiccation resistance, biofilm formation, and antibiotic susceptibility. Complementation studies with wild-type or mutated versions of HI_1017 can confirm phenotypic observations. Transcriptomic analysis comparing wild-type and knockout strains can identify compensatory mechanisms and affected pathways. Fluorescently-tagged HI_1017 can reveal subcellular localization patterns and potential redistribution under stress conditions. Interaction studies using pull-down assays coupled with mass spectrometry can identify protein partners that may provide functional context.

What purification strategy yields the highest purity and activity for recombinant HI_1017?

For optimal purification of His-tagged HI_1017, a multi-step chromatography approach is recommended. Initial capture should utilize immobilized metal affinity chromatography (IMAC) with Ni-NTA resin under native conditions with gentle detergents (e.g., 0.1% n-Dodecyl β-D-maltoside) to maintain protein folding. This should be followed by size exclusion chromatography to separate aggregates and ensure monodispersity. Ion exchange chromatography can be employed as a polishing step to achieve >90% purity . Critical parameters include maintaining pH at 8.0 throughout purification and including protease inhibitors to prevent degradation. For functional studies, incorporation of the purified protein into nanodiscs or amphipols can preserve native-like membrane environments. Quality control should include SDS-PAGE analysis, dynamic light scattering to assess homogeneity, and circular dichroism to verify proper folding.

How can researchers develop effective antibodies against HI_1017 for detection and localization studies?

Developing specific antibodies against HI_1017 requires careful epitope selection. Researchers should analyze the protein sequence to identify antigenic regions that are surface-exposed and unique to HI_1017 to avoid cross-reactivity with other aquaporins. For polyclonal antibodies, immunization protocols using recombinant full-length His-tagged HI_1017 can generate broad epitope recognition. For monoclonal antibodies, synthetic peptides corresponding to extracellular loops offer better specificity. Antibody validation should include Western blotting against recombinant protein and native H. influenzae lysates, immunoprecipitation tests, and pre-absorption controls. For immunolocalization, optimal fixation conditions must be established that preserve epitope accessibility while maintaining membrane structure. Super-resolution microscopy techniques like STORM or PALM combined with immunolabeling can precisely map HI_1017 distribution within bacterial cells.

What assay methods can quantitatively measure HI_1017 channel activity?

Quantitative assessment of HI_1017 channel activity requires multiple complementary approaches. Stopped-flow spectroscopy using proteoliposomes loaded with self-quenching fluorescent dyes (e.g., calcein) can measure water flux rates through changes in fluorescence intensity during osmotic challenges. Radioactive isotope tracing with ³H-labeled water can provide direct measurements of water movement. For potential solute transport, similar methods using fluorescent or radioactively labeled substrates should be employed. Single-channel recordings using patch-clamp techniques on reconstituted membranes can detect conductance events if HI_1017 permits ion passage. Mathematical modeling of transport kinetics should be applied to extract permeability coefficients. Temperature dependence studies (Arrhenius plots) can distinguish between channel-mediated transport and simple diffusion across membranes.

How does HI_1017 compare structurally and functionally to characterized aquaporins from other organisms?

Comparative analysis of HI_1017 with characterized aquaporins should examine several key features. Sequence alignment with canonical aquaporins from bacteria, mammals (particularly AQP1), and plants can identify conserved functional motifs and divergent regions. Phylogenetic analysis can place HI_1017 within the broader context of aquaporin evolution. The arrangement of transmembrane domains and conservation of the characteristic hourglass fold should be examined through structural modeling. Particular attention should be paid to the selectivity filter region, including the ar/R (aromatic/arginine) constriction site and NPA motifs, which determine substrate specificity. Functional comparisons should include water permeability measurements, selectivity for other substrates, pH sensitivity, and regulation mechanisms. These analyses can help determine whether HI_1017 represents a novel functional class within the aquaporin superfamily.

What genomic and proteomic approaches can identify potential functional partners of HI_1017?

To identify functional partners of HI_1017, researchers should employ a multi-omics approach. Genomic context analysis examining the organization of genes surrounding HI_1017 in the H. influenzae genome can reveal functionally related genes through operonic arrangements or conserved proximity. Transcriptomic analysis using RNA-seq under various stress conditions can identify genes co-regulated with HI_1017. Protein-protein interaction studies using pull-down assays with His-tagged HI_1017 followed by mass spectrometry can directly identify physical interactors. Bacterial two-hybrid screening can detect binary interactions. Cross-linking experiments followed by proteomic analysis can capture transient interactions. Bioinformatic prediction of protein interaction networks using tools like STRING or KEGG pathway analysis can guide experimental verification. Functional association studies should examine effects of HI_1017 deletion on global proteome composition.

What evolutionary insights can be gained from studying HI_1017 across different Haemophilus strains?

Evolutionary analysis of HI_1017 across Haemophilus species and strains can provide valuable insights into its functional importance. Researchers should sequence and compare HI_1017 homologs from multiple clinical and environmental isolates of H. influenzae and related Haemophilus species. Calculation of non-synonymous to synonymous substitution ratios (dN/dS) can identify regions under purifying or diversifying selection. Conservation analysis of transmembrane domains versus loop regions can highlight functionally critical regions. Genomic island analysis can determine if HI_1017 was horizontally acquired or represents an ancestral trait. Correlation studies between HI_1017 sequence variants and strain-specific phenotypes (biofilm formation, antibiotic resistance, virulence) can suggest functional roles. Reconstruction of ancestral sequences can track the evolutionary trajectory of this aquaporin-like protein within the Pasteurellaceae family.

What methodologies can assess the role of HI_1017 in Haemophilus influenzae pathogenesis?

To investigate HI_1017's potential role in pathogenesis, researchers should generate isogenic knockout mutants in virulent H. influenzae strains. These mutants should be evaluated in multiple infection models, including cell culture adhesion/invasion assays, biofilm formation on respiratory epithelial cells, and resistance to serum killing. Animal models of otitis media, pneumonia, or meningitis (depending on the strain's typical disease association) can assess virulence differences in vivo. Complementation studies with wild-type and mutant variants of HI_1017 can confirm phenotypic observations. Transcriptomic and proteomic analyses comparing wild-type and knockout strains during infection can identify affected virulence pathways. Immunohistochemistry using HI_1017-specific antibodies can track protein expression during different infection stages. Stress response experiments examining survival under host-relevant conditions (oxidative stress, nutrient limitation, antimicrobial peptides) can link HI_1017 function to pathogen survival strategies.

How might HI_1017 contribute to antibiotic resistance or tolerance in Haemophilus influenzae?

The potential role of HI_1017 in antibiotic resistance requires systematic investigation. Researchers should compare minimum inhibitory concentrations (MICs) of various antibiotic classes between wild-type and HI_1017 knockout strains. Time-kill curves can reveal differences in killing kinetics that might indicate tolerance rather than resistance. Persister cell formation assays can determine if HI_1017 contributes to this phenotype. If HI_1017 affects antibiotic susceptibility, uptake studies using fluorescently labeled or radioactive antibiotics can determine if the mechanism involves reduced permeability. Membrane integrity measurements using fluorescent dyes can assess if HI_1017 maintains membrane homeostasis under antibiotic stress. Expression analysis of HI_1017 following antibiotic exposure can reveal regulatory responses. Structure-function studies with site-directed mutagenesis can identify specific protein regions involved in any observed resistance phenotypes.

What is the potential of HI_1017 as a therapeutic target for treating Haemophilus influenzae infections?

Evaluating HI_1017 as a therapeutic target requires assessment of several criteria. Target validation studies should confirm that HI_1017 is essential for virulence or survival under in vivo conditions. Conservation analysis across clinical isolates can determine if HI_1017 represents a broadly applicable target. Structural studies focusing on unique features not present in human aquaporins can identify potential binding sites for selective inhibitors. High-throughput screening approaches using proteoliposome-based transport assays can identify small molecule inhibitors. Lead compounds should be evaluated for binding affinity, inhibitory potency, and selectivity versus human aquaporins. In vitro and in vivo efficacy studies should measure antibacterial activity and infection clearance. Resistance development studies through serial passage experiments can assess the barrier to resistance. Combination studies with conventional antibiotics can identify potential synergistic effects.

How can single-molecule techniques be applied to study HI_1017 dynamics and gating mechanisms?

Advanced single-molecule techniques offer unprecedented insights into HI_1017 function. Single-molecule FRET (smFRET) with strategically placed fluorophores can track conformational changes during transport events in real-time. Total internal reflection fluorescence (TIRF) microscopy of labeled protein in supported lipid bilayers can monitor distributional dynamics and oligomerization states. Atomic force microscopy (AFM) can directly visualize topological changes and measure mechanical properties of the protein. High-speed AFM can capture conformational transitions during substrate transport. Optical tweezers or magnetic tweezers can apply controlled forces to study mechanical gating mechanisms. Single-molecule tracking in live bacteria expressing fluorescently-labeled HI_1017 can reveal mobility and clustering behavior in native membranes. These approaches require careful protein engineering to introduce labeling sites without compromising function and sophisticated data analysis to extract meaningful kinetic and thermodynamic parameters.

What computational approaches can predict substrate specificity and transport mechanisms of HI_1017?

Computational approaches provide powerful tools for understanding HI_1017 function. Researchers should begin with homology modeling based on known aquaporin structures, followed by refinement through molecular dynamics (MD) simulations in explicit membrane environments. Potential of mean force calculations can determine energy barriers for different substrates along the transport pathway. Quantum mechanics/molecular mechanics (QM/MM) methods can investigate proton exclusion mechanisms. Machine learning approaches trained on characterized aquaporins can predict substrate preferences based on pore-lining residues. Coarse-grained simulations can access longer timescales necessary to observe complete transport events. Virtual screening campaigns against the modeled structure can identify potential inhibitors. Brownian dynamics simulations can model ion or water movement through the channel. These computational predictions should guide experimental mutagenesis studies to verify the importance of key residues in substrate selectivity and transport kinetics.

How does the regulation of HI_1017 expression differ under various environmental stresses?

Understanding HI_1017 regulation requires systematic analysis under different conditions. Researchers should employ quantitative PCR and Western blotting to measure mRNA and protein levels, respectively, under various stresses including osmotic shock, pH changes, nutrient limitation, oxidative stress, and antibiotic exposure. Transcriptional regulation can be investigated through promoter-reporter fusions and chromatin immunoprecipitation (ChIP-seq) to identify transcription factor binding sites. Post-transcriptional regulation should be examined through RNA stability assays and investigation of potential small RNAs using RNA-seq. Post-translational regulation can be assessed through phosphoproteomic analysis and other modification-specific detection methods. Environmental sensing mechanisms can be investigated through two-component system mutants and signal transduction pathway inhibitors. Integration with global stress response networks can be mapped through systems biology approaches combining transcriptomics, proteomics, and metabolomics data. This comprehensive analysis can reveal how H. influenzae modulates HI_1017 expression to adapt to environmental challenges.

What are the key structural differences between HI_1017 and human aquaporins?

The following table presents a comparative analysis of structural features between HI_1017 and human aquaporins:

This comparison highlights structural features unique to HI_1017 that may serve as targets for selective inhibition and provides insights into potential functional differences.

What experimental conditions yield optimal expression of recombinant HI_1017?

This table provides a comprehensive overview of expression and purification parameters that researchers can optimize when working with recombinant HI_1017.

How does HI_1017 function compare with other bacterial aquaporins in transport assays?

This comparative analysis highlights the unique transport profile of various bacterial aquaporins and outlines the methodology researchers should employ to characterize HI_1017 transport properties.