Recombinant Haemophilus influenzae UPF0070 protein HI_0370 (HI_0370)

What is Recombinant Haemophilus influenzae UPF0070 protein HI_0370?

Recombinant Haemophilus influenzae UPF0070 protein HI_0370 is a full-length protein consisting of 204 amino acids that can be expressed in heterologous systems such as E. coli with fusion tags for purification purposes. This protein belongs to the UPF0070 protein family, which is a group of uncharacterized protein families with conserved sequences across bacterial species. The protein is also known by alternative names including "Ancillary SecYEG translocon subunit" and "Periplasmic chaperone YfgM," suggesting its potential role in protein secretion and membrane protein assembly . The UniProt ID for this protein is P43989, which serves as a reference point for researchers examining protein characteristics and evolutionary relationships.

The recombinant version of this protein typically includes affinity tags, most commonly an N-terminal histidine tag, which facilitates purification using affinity chromatography techniques. The expression in E. coli systems enables researchers to obtain sufficient quantities of the protein for various analytical and functional studies. Understanding the basic properties of this protein is essential for developing experimental approaches to investigate its structure and function.

How does UPF0070 protein HI_0370 relate to bacterial physiology and pathogenesis?

While the precise function of UPF0070 protein HI_0370 remains to be fully elucidated, its annotation as an "Ancillary SecYEG translocon subunit" suggests involvement in protein translocation across the bacterial membrane . The SecYEG translocon is a conserved machinery responsible for protein secretion and membrane protein insertion, processes vital for bacterial survival and virulence. As a potential component of this system, HI_0370 may contribute to the proper folding or assembly of secreted virulence factors.

In the context of Haemophilus influenzae pathogenesis, proper protein secretion and membrane integrity are crucial for colonization and infection. By comparison to other H. influenzae virulence factors like Lipoprotein e (P4), which plays roles in heme acquisition and NAD utilization , ancillary proteins of the secretion machinery may indirectly affect pathogenesis by ensuring the proper localization of direct virulence determinants. For instance, P4 has been implicated in invasive disease pathogenesis in animal models, and proteins involved in its proper secretion could therefore impact virulence.

Research strategies to investigate the role of HI_0370 in pathogenesis might include generating knockout mutants and assessing their ability to cause disease in appropriate animal models, similar to approaches used for studying other H. influenzae proteins. Additionally, transcriptomic and proteomic analyses comparing wild-type and mutant strains could reveal affected pathways and potential interaction partners.

What expression systems are optimal for producing recombinant UPF0070 protein HI_0370?

E. coli expression systems represent the preferred platform for recombinant production of UPF0070 protein HI_0370, offering advantages of rapid growth, high protein yields, and established protocols. Commonly used E. coli strains for recombinant protein expression include BL21(DE3), which lacks proteases that might degrade the target protein, and Rosetta strains, which provide additional tRNAs for rare codons that might be present in the Haemophilus influenzae sequence . Expression vectors featuring T7 or tac promoters, combined with appropriate fusion tags (particularly His-tags), facilitate controlled induction and subsequent purification.

Expression optimization typically begins with small-scale cultures testing various induction conditions, including IPTG concentration (0.1-1.0 mM), induction temperature (16-37°C), and induction duration (4-24 hours). Lower temperatures (16-25°C) often improve proper protein folding by slowing the expression rate, especially important for membrane-associated proteins like HI_0370. For membrane-associated proteins that may be toxic or form inclusion bodies, specialized E. coli strains like C41(DE3) or C43(DE3) designed for membrane protein expression may prove beneficial.

Alternative expression systems including yeast (Pichia pastoris or Saccharomyces cerevisiae) might be considered if E. coli expression yields insufficient quantities of properly folded protein. These eukaryotic systems can sometimes provide improved folding environments and post-translational processing. Based on the successful expression reported for both UPF0070 protein HI_0370 and other bacterial proteins like UPF0270 protein NTHI1129 in heterologous systems, researchers have multiple viable options for expression optimization .

What purification strategies yield highest purity and activity for UPF0070 protein HI_0370?

A multi-step purification strategy typically yields the highest purity for recombinant UPF0070 protein HI_0370. The initial purification step leverages the N-terminal His-tag through immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins . Optimization of this step includes testing various imidazole concentrations in binding and washing buffers (10-50 mM) to minimize non-specific binding while maintaining target protein retention. Elution with an imidazole gradient (100-500 mM) typically releases the His-tagged protein with good initial purity.

Secondary purification steps may include size exclusion chromatography (SEC) to separate monomeric protein from aggregates and remove remaining contaminants. For UPF0070 protein HI_0370, Superdex 75 or Superdex 200 columns are appropriate choices based on the protein's molecular weight (approximately 22 kDa plus the tag). Ion exchange chromatography provides another orthogonal purification step, with the selection of cation or anion exchange resins depending on the protein's theoretical isoelectric point.

Throughout the purification process, protein activity should be monitored if functional assays are available. For membrane-associated proteins like HI_0370, maintaining an appropriate buffer environment is crucial - typically including mild detergents or lipid nanodiscs to mimic the native membrane environment if the protein is demonstrated to have membrane association. Final purity assessment by SDS-PAGE should demonstrate >90% purity, matching the standards reported for commercially available preparations .

What are the optimal storage conditions to maintain stability of recombinant UPF0070 protein HI_0370?

Long-term stability of recombinant UPF0070 protein HI_0370 is best achieved through proper storage conditions that prevent degradation and maintain functional conformation. Lyophilization represents an effective approach for extended storage, with the lyophilized powder demonstrating significantly higher stability than liquid formulations . For lyophilized preparations, storage at -20°C or -80°C is recommended, with expected shelf life of approximately 12 months under these conditions.

For working solutions, aliquoting is essential to avoid repeated freeze-thaw cycles, which can significantly reduce protein activity. Small working aliquots can be stored at 4°C for up to one week, while longer-term storage requires -20°C or -80°C temperatures . The addition of glycerol to a final concentration of 5-50% (optimally 50%) helps prevent ice crystal formation during freezing, protecting protein structure and function. Buffer composition also significantly impacts stability, with Tris/PBS-based buffers at pH 8.0 containing approximately 6% trehalose serving as effective stabilizers for UPF0070 protein HI_0370 .

When reconstituting lyophilized protein, brief centrifugation is recommended to bring contents to the bottom of the vial, followed by addition of deionized sterile water to achieve concentrations of 0.1-1.0 mg/mL. This methodical approach to storage and reconstitution maximizes protein stability and extends usable lifetime, crucial considerations for research applications requiring consistent protein quality across multiple experiments.

What analytical techniques are most informative for characterizing UPF0070 protein HI_0370?

Comprehensive characterization of UPF0070 protein HI_0370 requires multiple complementary analytical techniques. SDS-PAGE represents the foundational method for purity assessment and approximate molecular weight determination, with expected band position corresponding to approximately 22 kDa plus any fusion tags . Western blotting using antibodies against either the His-tag or the protein itself provides higher specificity for identity confirmation. For precise molecular mass determination, mass spectrometry techniques such as MALDI-TOF or ESI-MS should be employed.

Circular dichroism (CD) spectroscopy provides valuable insights into secondary structure composition, distinguishing alpha-helical, beta-sheet, and random coil elements. This information helps validate proper folding of the recombinant protein compared to predicted structural elements. Size exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) determines oligomeric state and homogeneity in solution, critical parameters for functional studies and crystallization attempts.

For membrane-associated proteins like UPF0070 protein HI_0370, techniques assessing membrane interaction are particularly relevant. These include liposome binding assays, surface plasmon resonance (SPR) with immobilized lipid bilayers, and fluorescence-based assays measuring protein-membrane interactions. Additionally, limited proteolysis experiments coupled with mass spectrometry can identify flexible regions and domains, informing structural models and guiding protein engineering efforts. The systematic application of these techniques provides a comprehensive biophysical profile essential for understanding protein function and designing meaningful functional assays.

How can interaction studies reveal functional partners of UPF0070 protein HI_0370?

As an "Ancillary SecYEG translocon subunit," UPF0070 protein HI_0370 likely participates in protein-protein interactions crucial to its function . Multiple complementary approaches can identify and characterize these interactions. Pull-down assays using His-tagged HI_0370 as bait, followed by mass spectrometry analysis of co-precipitated proteins from Haemophilus influenzae lysates, represent a straightforward approach to identifying potential binding partners. This technique can be enhanced using chemical crosslinking to stabilize transient interactions before purification.

Yeast two-hybrid (Y2H) screening offers an alternative approach, though membrane-associated proteins like HI_0370 may require modified membrane-based Y2H systems. For targeted hypothesis testing, surface plasmon resonance (SPR) or isothermal titration calorimetry (ITC) provide quantitative binding parameters (KD, kon, koff, ΔH, ΔS) for specific protein pairs. Microscale thermophoresis (MST) offers an alternative requiring smaller sample volumes for interaction analysis.

In-cell approaches include bacterial two-hybrid assays and fluorescence resonance energy transfer (FRET) studies using fluorescently labeled proteins. For studying membrane-associated complexes, techniques like native PAGE or blue native PAGE preserve protein complexes during separation. When applying these methods, controls must address potential artifacts from the recombinant expression system and fusion tags, ideally confirming interactions through multiple independent techniques and ultimately in the native Haemophilus influenzae environment through techniques like co-immunoprecipitation with antibodies against the native proteins.

What functional assays can assess the proposed chaperone activity of UPF0070 protein HI_0370?

Given its annotation as a "Periplasmic chaperone YfgM," functional assays for UPF0070 protein HI_0370 should focus on its potential chaperone activities . Thermal aggregation assays represent a straightforward approach, wherein the ability of HI_0370 to prevent aggregation of model substrate proteins (such as citrate synthase or luciferase) during thermal denaturation is measured by light scattering or centrifugation followed by SDS-PAGE analysis. Various molar ratios of HI_0370 to substrate proteins should be tested to establish concentration-dependent effects.

Enzymatic activity protection assays measure HI_0370's ability to maintain the functional activity of substrate enzymes under stress conditions (elevated temperatures or chemical denaturants like urea). For proteins with specific periplasmic substrates in Haemophilus influenzae, refolding assays can determine whether HI_0370 enhances the recovery of active protein from denatured states. This typically involves denaturing a reporter protein in urea or guanidinium chloride, then measuring activity recovery during dilution in the presence or absence of HI_0370.

In vivo functional complementation provides perhaps the most biologically relevant assessment. This approach involves creating HI_0370 deletion mutants in Haemophilus influenzae and measuring phenotypes related to membrane protein assembly, stress tolerance, or virulence. Subsequent complementation with wild-type or mutant versions of HI_0370 can confirm functional relationships. Monitoring the accumulation of misfolded proteins in the periplasm or membrane fractions of wild-type versus knockout strains provides additional evidence for chaperone activity. These combined approaches would establish whether HI_0370 functions similarly to other periplasmic chaperones like Skp or SurA in Gram-negative bacteria.

How does UPF0070 protein HI_0370 compare to homologous proteins in other bacterial species?

Phylogenetic analysis can identify clades within the UPF0070 family that might represent functional diversification. Structural comparisons using available crystal structures or homology models highlight conserved surface patches that potentially represent interaction sites with partner proteins or substrates. Particularly interesting is comparative genomic context analysis - examining the organization of genes surrounding yfgM/HI_0370 orthologs across species may reveal conserved operons or genetic linkage with specific cellular pathways.

The UPF0070 protein in Haemophilus influenzae likely shares functional characteristics with homologs in other pathogenic bacteria, potentially contributing to membrane protein homeostasis during infection. Comparative analysis with UPF0270 protein NTHI1129, another uncharacterized protein family in H. influenzae , might reveal whether these different UPF families have related or distinct functions in bacterial physiology. This evolutionary perspective guides hypothesis generation about specific functional roles and informs experimental design for future studies.

What role might UPF0070 protein HI_0370 play in bacterial stress response?

As a potential periplasmic chaperone, UPF0070 protein HI_0370 may participate in bacterial stress response pathways, particularly those involving envelope stress. Comparison with other bacterial systems suggests possible involvement in monitoring and maintaining membrane protein homeostasis during environmental challenges. This hypothesis is indirectly supported by research on heat shock proteins (HSPs) like Hsp70, which function as molecular chaperones during stress conditions . Though UPF0070 is not an Hsp70 family member, its potential chaperone function suggests analogous protective roles during stress.

Experimental investigation of this hypothesis would involve stress exposure experiments comparing wild-type and HI_0370 knockout strains of Haemophilus influenzae. Stressors to test would include elevated temperatures, oxidative stress (H₂O₂), osmotic stress, and relevant antimicrobial compounds. Phenotypic assays would measure survival rates, growth kinetics, and biofilm formation under these conditions. Transcriptomic analysis comparing gene expression profiles between wild-type and knockout strains during stress exposure could identify affected pathways and potential compensatory mechanisms.

Protein-level investigations should examine whether HI_0370 expression changes during stress conditions and if the protein undergoes stress-induced relocalization or modifications. Proteomics approaches could identify differences in the complement of membrane and periplasmic proteins between wild-type and knockout strains during stress, potentially revealing specific substrates that depend on HI_0370 for proper folding or localization. Understanding HI_0370's role in stress response has implications for bacterial pathogenesis, as stress adaptation is crucial during host colonization and infection.

How does site-directed mutagenesis inform structure-function relationships in UPF0070 protein HI_0370?

Site-directed mutagenesis represents a powerful approach for dissecting structure-function relationships in UPF0070 protein HI_0370. Strategic mutation design should target conserved residues identified through multiple sequence alignments of UPF0070 family proteins, focusing on charged or aromatic amino acids likely involved in protein-protein interactions or membrane association. Additionally, predicted secondary structure elements and potential functional motifs should be systematically disrupted to assess their contribution to protein function.

The experimental workflow begins with generating a panel of point mutations using PCR-based methods on the recombinant expression construct. Following expression and purification under identical conditions to wild-type protein, comparative characterization should assess effects on: (1) protein stability through thermal denaturation assays, (2) secondary structure through circular dichroism, (3) oligomeric state through size exclusion chromatography, and (4) membrane interaction through liposome binding assays. For functional assessment, in vitro chaperone activity assays comparing wild-type and mutant proteins would reveal residues essential for this proposed function.

In vivo complementation studies provide the most biologically relevant assessment of mutational effects. This involves introducing wild-type or mutant versions of HI_0370 into knockout strains of Haemophilus influenzae and measuring restoration of phenotypes related to membrane integrity, stress tolerance, or pathogenesis. Systematic application of this mutagenesis pipeline would generate a functional map of the protein, identifying domains involved in specific aspects of its function and potentially revealing novel functional motifs within the UPF0070 family.

What advanced structural biology approaches could resolve UPF0070 protein HI_0370 structure?

Determining the three-dimensional structure of UPF0070 protein HI_0370 requires strategic application of complementary structural biology techniques. X-ray crystallography represents a gold standard approach, though membrane-associated proteins like HI_0370 present crystallization challenges. Optimization strategies include screening numerous crystallization conditions with various precipitants, pH values, and additives. Protein engineering approaches such as surface entropy reduction (replacing flexible, high-entropy surface residues with alanine) or fusion with crystallization chaperones (T4 lysozyme or BRIL) may enhance crystallization propensity.

Cryo-electron microscopy (cryo-EM) offers an alternative route that has revolutionized membrane protein structural biology. For smaller proteins like HI_0370 (~22 kDa), strategies to overcome size limitations include focusing on larger complexes with interaction partners or utilizing techniques like scaffold-based cryo-EM. Nuclear magnetic resonance (NMR) spectroscopy presents another viable approach, particularly suitable for proteins under 25 kDa, providing not only structural information but also insights into dynamics. This would require isotopic labeling (¹³C, ¹⁵N) during recombinant expression.

How can UPF0070 protein HI_0370 research contribute to understanding bacterial pathogenesis?

Research on UPF0070 protein HI_0370 has significant implications for understanding Haemophilus influenzae pathogenesis through several mechanisms. As a potential component of the protein secretion machinery (SecYEG translocon) and periplasmic chaperone, HI_0370 may facilitate proper folding and localization of virulence factors . By ensuring correct membrane protein assembly, it could maintain bacterial envelope integrity during host colonization and immune evasion. Comparative studies with other H. influenzae virulence factors like Lipoprotein e (P4), which plays established roles in heme acquisition and invasive disease pathogenesis , could reveal whether HI_0370 interacts with or affects the localization of such direct virulence determinants.

Experimental approaches to explore this relationship include generating conditional knockout strains of HI_0370 and assessing their ability to cause disease in appropriate animal models. Virulence assays would measure parameters such as bacterial burden in tissues, inflammatory responses, and survival rates compared to wild-type infections. Transcriptomic and proteomic analyses comparing wild-type and mutant strains during infection could identify affected virulence pathways. Of particular interest would be examining whether HI_0370 deficiency alters the localization or abundance of known virulence factors in the bacterial membrane or secretome.

The therapeutic implications of this research extend to potential drug development targeting bacterial secretion machinery. If HI_0370 proves essential for pathogenesis, it could represent a novel antibiotic target with potential broad-spectrum applications across related bacteria. Understanding the fundamental biology of membrane protein assembly and secretion in pathogens opens avenues for innovative antimicrobial strategies addressing the growing challenge of antibiotic resistance.

What are emerging techniques for studying membrane-associated proteins like UPF0070 protein HI_0370?

The study of membrane-associated proteins like UPF0070 protein HI_0370 benefits from rapidly evolving methodological innovations. Nanodiscs technology represents a significant advancement, providing a native-like phospholipid bilayer environment for membrane proteins without detergents. Various nanodisc systems including membrane scaffold protein (MSP) nanodiscs and polymer-based systems like styrene-maleic acid lipid particles (SMALPs) enable extraction of membrane proteins directly from native membranes while preserving their lipid environment. These systems enhance structural studies and functional assays by maintaining protein stability and native interactions.

Single-molecule techniques provide unprecedented insights into protein dynamics and heterogeneity. Single-molecule FRET (smFRET) can track conformational changes in real-time, while techniques like total internal reflection fluorescence (TIRF) microscopy allow visualization of individual protein molecules at membrane interfaces. For structural studies, advances in cryo-electron tomography enable visualization of proteins in their native cellular context at increasingly higher resolutions, potentially revealing HI_0370's precise localization within the bacterial envelope.

Computational approaches have also transformed membrane protein research. Enhanced molecular dynamics simulations with specialized force fields for membrane environments can model protein-lipid interactions and conformational dynamics across biologically relevant timescales. Machine learning approaches increasingly contribute to membrane protein structure prediction, functional annotation, and interaction network mapping. For proteins like HI_0370 with limited experimental characterization, these computational tools generate testable hypotheses about structure-function relationships. The integration of these emerging techniques promises to overcome traditional challenges in membrane protein research and accelerate understanding of proteins like UPF0070 HI_0370.

How can high-throughput approaches advance understanding of UPF0070 protein function?

High-throughput experimental strategies offer powerful approaches for systematically dissecting UPF0070 protein HI_0370 function. Protein interaction mapping through techniques like BioID or APEX proximity labeling can comprehensively identify the protein's interaction network within the bacterial cell. These methods involve fusing HI_0370 with a biotin ligase that biotinylates proximal proteins, which are subsequently purified and identified by mass spectrometry. This approach reveals not only stable interaction partners but also transient associations and nearby proteins in the cellular microenvironment.

Genome-wide genetic interaction screens provide complementary functional insights. Techniques like transposon sequencing (Tn-seq) or CRISPR interference (CRISPRi) in combination with HI_0370 deletion identify synthetic lethal or synthetic sick interactions - genes whose disruption is particularly detrimental when combined with HI_0370 deficiency. Such genetic relationships often indicate functional connections or parallel pathways. Phenotypic microarrays testing growth across hundreds of conditions simultaneously can identify specific environmental stresses or nutrients that differentially affect wild-type versus HI_0370 mutant strains.

For mechanistic studies, high-throughput mutagenesis approaches like deep mutational scanning combine comprehensive mutagenesis with functional selection and next-generation sequencing. This generates fitness landscapes across thousands of protein variants simultaneously, identifying residues critical for various aspects of protein function. When applied to UPF0070 protein HI_0370, these approaches would rapidly accelerate functional annotation, generating rich datasets that inform focused mechanistic studies. Integration of these high-throughput datasets with structural information and computational models would provide a systems-level understanding of HI_0370's role in bacterial physiology and pathogenesis.