Recombinant Burkholderia mallei Protease HtpX homolog (htpX)
Description
Introduction to Burkholderia mallei and HtpX
Burkholderia mallei is a gram-negative bacterium that causes glanders, one of the most dangerous zoonotic diseases affecting solipeds. As a category B select agent in the United States, B. mallei must be studied under BSL3 containment conditions . This pathogen is closely related to Burkholderia pseudomallei, with approximately 99.5% DNA-DNA sequence identity between orthologous genes . Both pathogens are considered significant bioterrorism threats due to their virulence, infectivity, and limited treatment options.
The protease HtpX homolog represents an important bacterial enzyme encoded by the htpX gene in B. mallei. This enzyme belongs to the M48 peptidase family of metalloproteases and plays significant roles in protein quality control and stress response mechanisms. The increasing interest in HtpX stems from its potential as a diagnostic marker, therapeutic target, and tool for understanding B. mallei pathogenesis.
Gene Structure and Organization
The htpX gene in B. mallei is found as a conserved locus across different strains. In B. mallei strain NCTC 10247, the gene is designated as BMA10247_2356, while in strain SAVP1, it is identified as BMASAVP1_A2802 . The coding sequence for htpX spans 909 base pairs, encoding a protein of 290 amino acid residues with no signal peptide .
The htpX gene appears to be highly conserved among Burkholderia species, with significant homology between the proteins encoded by B. mallei and B. pseudomallei. This conservation suggests an essential role for HtpX in Burkholderia biology and potentially in pathogenesis.
Three-Dimensional Structure
The three-dimensional structure of the HtpX protease has been predicted using computational methods like AlphaFold. Analysis reveals that the model of the B. mallei HtpX protease consists of ten α-helixes, four strands, two 310 helixes, twelve turns, seven bends, and multiple coil regions . This complex structure is essential for its proteolytic functions and substrate interactions.
Active Site and Metal Ion Binding
The HtpX protease from B. mallei functions as a zinc-dependent metalloprotease. The active site contains a characteristic HEXXH motif typical of metalloproteases, where the two histidine residues coordinate a zinc ion, and the glutamic acid participates in catalysis.
Research on HtpX homologs indicates that metal ion binding significantly affects the structure and function of the enzyme. Studies have shown that Ca2+, Zn2+, Cl−, and K+ binding to recombinant HtpX can change the 3D structure and active sites of the protease . Among these, Ca2+ binding to HtpX helps to obtain the largest active pocket, potentially enhancing its catalytic efficiency.
Binding Pocket Analysis
Detailed analysis of the binding pockets of HtpX reveals significant structural features that influence substrate recognition and catalysis. The following table summarizes the binding pocket characteristics of HtpX with different ions:
| Protease Form | Area (Ų) | Volume (ų) | Number of Active Sites |
|---|---|---|---|
| HtpX alone | 557.472 | 837.241 | 41 |
| HtpX-Ca²⁺ | 918.154 | 1378.221 | 38 |
| HtpX-Cl⁻ | 714.286 | 867.364 | 39 |
| HtpX-K⁺ | 925.544 | 1335.237 | 41 |
| HtpX-Zn²⁺ | 811.023 | 1179.127 | 37 |
This data demonstrates that Ca²⁺ binding creates the largest pocket volume, potentially enhancing substrate accommodation and enzyme efficiency .
Enzymatic Activity and Catalytic Mechanism
The HtpX protease functions as an intramembrane protease, cleaving transmembrane substrates to regulate various cellular processes. As a member of the M48 peptidase family, it plays critical roles in protein quality control, particularly in the degradation of misfolded membrane proteins.
The catalytic mechanism involves a zinc-dependent hydrolysis of peptide bonds. The active site zinc ion is coordinated by two histidine residues from the HEXXH motif, with the glutamic acid functioning as a catalytic base to activate a water molecule for nucleophilic attack on the peptide bond.
Temperature and pH Dependence
Studies on recombinant HtpX proteases indicate that they typically exhibit optimal activity at neutral pH and moderate temperatures. Research on related HtpX proteases demonstrates that the optimal reaction temperature is around 45°C, with enzyme activity doubling compared to 30°C . The enzyme shows strong temperature tolerance, with activity preservation rates over 90% at 50°C for 8 hours, but severe activity decrease at temperatures above 60°C for extended periods.
The optimal pH for HtpX activity is approximately 7, with high enzyme activity maintained within the pH 7-9 range. After storage in pH 6 buffer for 8 hours, the enzyme activity preservation rate is highest, while storage under more acidic or alkaline conditions leads to more severe inactivation . These characteristics classify HtpX as a neutral and heat-resistant metalloprotease.
Expression Systems
Recombinant expression of B. mallei HtpX has been achieved in several systems. The most common approach involves cloning the htpX gene into suitable expression vectors followed by transformation into bacterial expression hosts. For instance, plasmids like pHT43 have been used for recombinant expression, with the gene cloned into restriction sites such as BamHI and SmaI .
Expression hosts like Escherichia coli BL21(DE3) and Bacillus subtilis WB800N have been successfully employed for HtpX production. In these systems, expression is typically induced using IPTG (Isopropyl β-D-1-thiogalactopyranoside) at a final concentration of 1 mM .
Purification and Characterization
After expression, the recombinant HtpX protein can be purified using various chromatographic techniques. SDS-PAGE analysis typically reveals a protein band of approximately 42 kDa, consistent with the expected size of the HtpX protease .
Characterization of the purified recombinant HtpX involves assessing its enzymatic activity, substrate specificity, and dependence on environmental factors. Activity assays often utilize synthetic peptide substrates or proteins like azocasein to measure proteolytic activity. Enzyme activity is typically expressed in units, with one unit defined as the amount of enzyme that catalyzes the conversion of substrate under standard conditions.
HtpX in the Context of Bacterial Pathogenesis
Proteases, including HtpX, play crucial roles in bacterial pathogenesis by contributing to protein quality control, stress response, and potentially direct interactions with host proteins. In the context of B. mallei infection, HtpX may contribute to bacterial survival under stress conditions encountered during host infection.
Research on related bacterial pathogens suggests that metalloproteases like HtpX may be involved in degrading misfolded proteins that accumulate during stress, thereby maintaining cellular proteostasis. This function could be particularly important during infection when bacteria encounter host defense mechanisms and antimicrobial agents .
Diagnostic Applications
Recombinant B. mallei HtpX has potential applications in diagnostic tools for glanders detection. The protein can be used in enzyme-linked immunosorbent assays (ELISAs) for detecting B. mallei infections in animals and potentially humans . Such diagnostic methods are valuable for surveillance and control of this devastating disease.
Commercial ELISA kits utilizing recombinant HtpX have been developed for research purposes, with typical quantities of 50 μg available for diagnostic development and characterization . These tools can help in the rapid identification of B. mallei infection, contributing to better disease management and control.
Therapeutic Target Potential
As a metalloprotease involved in protein quality control, HtpX represents a potential target for therapeutic intervention. Inhibitors targeting bacterial metalloproteases have been explored as a strategy for developing novel antimicrobial agents. By disrupting essential proteolytic functions, such inhibitors could potentially compromise bacterial survival and virulence.
Research on metalloprotease inhibitors like batimastat has provided insights into potential approaches for targeting proteases like HtpX . Further studies exploring the specific inhibition of B. mallei HtpX could lead to the development of new therapeutic options for glanders, addressing the current limitations in treatment options.
Research Applications in Pathogenesis Studies
Recombinant HtpX serves as a valuable tool for studying B. mallei pathogenesis. By investigating the role of this protease in bacterial physiology and host-pathogen interactions, researchers can gain insights into the mechanisms underlying glanders disease progression and potential vulnerabilities that could be exploited for intervention.
The availability of purified recombinant HtpX facilitates studies on its substrate specificity, regulation, and potential interactions with host proteins. Such research contributes to a deeper understanding of B. mallei biology and pathogenesis, informing the development of countermeasures against this significant biothreat agent .
References
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Burkholderia pseudomallei and Burkholderia mallei are category B select agents and must be studied under BSL3 containment in the United States .
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Burkholderia mallei can be identified through various biochemical and molecular tests, including colony morphology, oxidase testing, and resistance to polymyxin B .
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Recombinant HtpX from B. mallei strain NCTC 10247 has been produced and characterized with ordered locus name BMA10247_2356 .
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Burkholderia pseudomallei and B. mallei represent significant biothreat agents with the potential for use in bioterrorism .
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Protease production by Burkholderia species does not necessarily correlate with virulence in mice when injected via the intraperitoneal route .
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The htpX gene encodes a metalloprotease with an M48 peptidase domain that is influenced by metal ion binding, particularly Ca²⁺ .
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B. mallei shares approximately 99.5% DNA-DNA sequence identity with B. pseudomallei orthologues .
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Recombinant expression of bacterial metalloproteases provides insights into their structure-function relationships .
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Recombinant HtpX from B. mallei strain SAVP1 has also been produced with ordered locus name BMASAVP1_A2802 .
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B. mallei and B. pseudomallei exhibit phenotypic differences that may relate to their distinct pathogenic mechanisms .
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them during order placement, and we will prepare accordingly.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please inform us in advance as additional fees may apply.
Generally, liquid forms have a shelf life of 6 months at -20°C/-80°C. Lyophilized forms have a shelf life of 12 months at -20°C/-80°C.
Target Background
KEGG: bmv:BMASAVP1_A2802
Q&A
What is the basic structure and function of Burkholderia mallei Protease HtpX homolog?
Burkholderia mallei Protease HtpX homolog is a membrane-bound metalloprotease that appears to be involved in protein quality control. Its amino acid sequence (MFNWVKTAMLMAAITAFLVIVIGGMIGGSGRGMTIALLIALGNMFFSYWFSDKMVLRMYNAQEVDEATAPQFYRMVRELATRANLPMPRVYLIDENQPNAFATGRNPEHAAVAATTGILRVLSEREMRGVMAHELAHVKHRDILISTISATMAGAISALANFAMFFGGRDENGRPANP) suggests transmembrane domains with characteristic metalloprotease motifs . The protein likely plays a role in degrading misfolded membrane proteins, similar to other HtpX homologs in bacterial systems. The structural analysis indicates it contains multiple transmembrane segments that anchor it within the bacterial membrane, with catalytic domains positioned to interact with substrate proteins.
What are the recommended storage and handling conditions for working with Recombinant HtpX?
For optimal experimental results, store the recombinant protein at -20°C, and for extended storage periods, maintain it at -20°C or -80°C . It's recommended to avoid repeated freeze-thaw cycles as this can compromise protein integrity and activity. For ongoing experiments, working aliquots can be stored at 4°C for up to one week . When handling the protein, maintain cold chain practices and use appropriate buffer conditions as specified in the product information (Tris-based buffer with 50% glycerol, optimized for this protein) . These storage conditions help preserve the structural integrity and enzymatic activity of the protease for experimental applications.
How does HtpX homolog compare between different Burkholderia mallei strains?
The recombinant HtpX homolog has been characterized from at least two different Burkholderia mallei strains: SAVP1 (Uniprot NO.: A1V794) and NCTC 10229 (Uniprot NO.: A2S8H2) . Sequence comparison reveals high conservation of the amino acid sequence between these strains, suggesting functional importance of this protease across different isolates. While the core functional domains appear to be preserved, researchers should be aware of potential strain-specific variations that might affect experimental outcomes. When designing comparative studies between strains, it's important to account for these potential variations and standardize experimental conditions accordingly.
What is the role of HtpX homolog in Burkholderia mallei virulence mechanisms?
While direct evidence for HtpX's role in B. mallei virulence is not fully established in the provided research, studies of related bacterial pathogens suggest potential involvement in stress response and pathogenesis. Similar to other membrane proteases, HtpX may contribute to bacterial adaptation during host infection by maintaining membrane protein homeostasis under stress conditions. Research on related Burkholderia species shows that membrane-associated proteins often play crucial roles in virulence. For instance, in Burkholderia pseudomallei, membrane-associated proteins like surface attachment protein (Sap1) are essential virulence factors . Experimental approaches to investigate HtpX's potential role in virulence could include gene knockout studies, virulence models, and comparative analysis of expression levels during infection.
How can researchers effectively express and purify functionally active HtpX for in vitro studies?
For successful expression and purification of functionally active HtpX, researchers should consider using specialized expression systems optimized for membrane proteins. Since HtpX is a membrane-bound metalloprotease, expression in E. coli systems with careful optimization of induction conditions (temperature, IPTG concentration) is recommended. Purification strategies should include detergent solubilization steps (such as DDM or LDAO) followed by affinity chromatography using the protein's tag. Drawing from techniques used for similar bacterial proteases, researchers might employ the mini-Tn7 integration system, which has been successfully used for Burkholderia protein expression studies . Activity assays should be conducted to confirm that the purified protein retains its proteolytic function, possibly using fluorescently labeled substrates designed based on predicted cleavage sites.
What protein-protein interactions might be significant for HtpX function in cellular contexts?
As a membrane-bound protease involved in protein quality control, HtpX likely interacts with multiple membrane and membrane-associated proteins. Potential interaction partners may include substrate misfolded proteins, other components of protein quality control machinery, and possibly regulatory proteins. Based on studies of related bacterial systems, HtpX may function in coordination with other proteases and chaperones to maintain membrane protein homeostasis. To identify these interactions, researchers could employ techniques such as bacterial two-hybrid systems, co-immunoprecipitation followed by mass spectrometry, or proximity labeling approaches. Understanding these interactions could reveal new insights into bacterial stress response mechanisms and potential therapeutic targets.
What are the optimal assay conditions for measuring HtpX protease activity?
When designing assays to measure HtpX protease activity, researchers should consider several key parameters. As a metalloprotease (EC= 3.4.24.-) , HtpX activity depends on metal ion cofactors, typically zinc. Optimal buffer conditions generally include Tris buffer (pH 7.5-8.0) with added zinc or other divalent cations. Temperature optimization is essential, with activity typically highest at 37°C (physiological temperature for Burkholderia). Substrate selection is critical - fluorogenic peptide substrates based on known cleavage sites of HtpX homologs are recommended. For kinetic measurements, researchers should establish linear reaction rates and determine Km and Vmax values. Control experiments should include metal chelators (like EDTA) to confirm metalloprotease activity and protease inhibitors to rule out contaminating protease activities.
How can researchers accurately evaluate the subcellular localization of HtpX in Burkholderia mallei?
For accurate subcellular localization studies of HtpX in Burkholderia mallei, researchers should employ multiple complementary approaches. Cellular fractionation techniques (separating cytoplasmic, periplasmic, membrane, and extracellular fractions) followed by Western blotting with HtpX-specific antibodies can provide initial localization data. For more detailed visualization, fluorescence microscopy using GFP-tagged HtpX or immunofluorescence with specific antibodies can reveal the distribution pattern within bacterial cells. When designing these experiments, researchers should be aware that membrane protein overexpression might lead to mislocalization artifacts. To confirm results, electron microscopy with immunogold labeling can provide high-resolution localization data. For work with pathogenic Burkholderia strains, consider using attenuated strains like Bp82 with appropriate biosafety measures as demonstrated in Burkholderia research protocols .
What controls and validation steps are essential when studying HtpX in cellular infection models?
When studying HtpX in cellular infection models, several controls and validation steps are essential. First, researchers should validate HtpX expression levels in the bacterial strains used for infection, comparing wildtype, mutant, and complemented strains. For gene knockout studies, complete deletion should be confirmed by PCR and Western blotting. Complementation controls are critical to confirm phenotypes are specifically due to HtpX loss. When using cell culture infection models, similar to those used for Burkholderia pseudomallei studies , researchers should include controls for bacterial entry (using cytochalasin D to block uptake) and perform gentamicin protection assays to distinguish intracellular from extracellular bacteria. Time-course experiments (2, 8, and 24 hours post-infection) help track the progression of infection . Additionally, microscopy-based validation of bacterial localization within host cells provides important confirmatory data.
What genetic engineering approaches are most effective for studying HtpX function in Burkholderia mallei?
For effective genetic manipulation of htpX in Burkholderia mallei, several approaches have proven successful in Burkholderia research. The allelic replacement method based on double homologous recombination is particularly effective, as demonstrated in Burkholderia studies . This approach allows for precise gene deletion or modification. For complementation studies, the mini-Tn7 integration system has been successfully used in Burkholderia species , allowing stable chromosomal integration of genes. When designing expression constructs, consider using inducible promoter systems like the lac promoter, which has been successfully employed in Burkholderia . For transient expression studies, broad-host-range vectors like pBLAC, which is derived from pMLBAD and can replicate in Burkholderia species, offer flexibility . Given the biosafety concerns with Burkholderia mallei, consider using attenuated strains or surrogate models when appropriate.
How can researchers effectively analyze HtpX expression under different environmental conditions?
To analyze HtpX expression under varying environmental conditions, researchers should employ a multi-faceted approach. Quantitative RT-PCR (qRT-PCR) provides precise measurement of htpX transcript levels and can validate findings from broader transcriptomic studies . For comprehensive expression analysis, RNA-Seq can reveal how htpX expression changes in response to different stressors (pH, temperature, nutrient limitation, antimicrobial agents) and during different growth phases. For protein-level analysis, Western blotting with HtpX-specific antibodies allows quantification of protein expression. To understand regulation, promoter-reporter fusions (using luciferase or fluorescent proteins) can monitor htpX promoter activity in real-time. For single-cell analysis of expression heterogeneity, techniques like single-cell transcriptomics or fluorescence microscopy with reporter constructs are valuable. Controls should include housekeeping genes for normalization and validation of RNA-Seq findings through qRT-PCR as demonstrated in Burkholderia research .
What approaches can be used to identify and characterize potential inhibitors of HtpX protease activity?
For identification and characterization of HtpX inhibitors, researchers can implement a systematic drug discovery pipeline. Initial high-throughput screening can utilize fluorescence-based protease assays with purified recombinant HtpX to identify compounds that reduce enzymatic activity. Structure-based virtual screening is another approach, leveraging homology models of HtpX to identify compounds predicted to bind the active site. Lead compounds should undergo dose-response testing to determine IC50 values. Secondary screening should assess selectivity by testing against other metalloproteases. For mechanism of action studies, enzyme kinetic analysis can determine if inhibition is competitive, non-competitive, or uncompetitive. Cellular assays should evaluate compound effectiveness in bacterial cultures, measuring growth inhibition and changes in protein homeostasis. For promising inhibitors, binding affinity and mechanisms can be further characterized using techniques like isothermal titration calorimetry or surface plasmon resonance. Ultimately, lead compounds should be evaluated in infection models to assess their potential as therapeutic agents.
