Recombinant Neisseria meningitidis serogroup C Glucokinase (glk)
Description
Definition and Functional Role
Glucokinase (Glk) catalyzes the ATP-dependent phosphorylation of glucose to glucose-6-phosphate, the first step in glycolysis and alternative pathways like the Entner-Doudoroff (ED) or pentose phosphate pathway (PPP). In N. meningitidis, Glk (encoded by NMV_1004) is essential for glucose catabolism, as demonstrated by growth inhibition in glucose-containing media upon gene deletion .
The recombinant form (Product Code: CSB-EP009319NEW) is expressed in Escherichia coli and purified to >85% homogeneity, retaining enzymatic activity for biochemical studies .
Enzymatic Activity and Pathway Integration
Glk operates within a glucose utilization operon regulated by the HexR transcriptional repressor . Key findings:
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Catalytic efficiency: Purified Glk exhibits Vmax = 12 μmol/min/mg at pH 7.5, optimal for meningococcal intracellular conditions .
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Pathway branching: Glucose-6-P generated by Glk feeds into either:
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Regulation: HexR represses the Glk operon (NMV_1002–NMV_1007) in the absence of glucose, derepressing transcription 8-fold upon glucose availability .
Metabolic Studies
Recombinant Glk enables in vitro reconstitution of meningococcal glucose metabolism. Experiments using purified enzymes (e.g., glucose-6-P dehydrogenase, gluconate-6-P dehydrogenase) confirmed pathway flux toward ED or PPP based on substrate availability .
Virulence Implications
While Glk itself is not a virulence factor, its role in central metabolism influences pathogen survival:
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HexR-regulated Glk expression enhances bacterial fitness in blood (glucose-rich environment) .
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Mutants lacking Glk show attenuated growth in minimal media, suggesting metabolic adaptability is critical for infection .
Future Directions
Current research gaps include:
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Structural resolution of Glk to identify allosteric regulatory sites.
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Screening for Glk inhibitors as potential antimicrobial agents.
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Elucidating cross-talk between Glk-dependent pathways and virulence gene expression .
This enzyme remains a pivotal tool for dissecting meningococcal metabolism and developing targeted therapies.
Product Specs
Target Background
KEGG: nmn:NMCC_1305
Q&A
What is the role of glucokinase in N. meningitidis serogroup C metabolism?
Glucokinase (glk) in N. meningitidis catalyzes the phosphorylation of glucose to glucose-6-phosphate, representing the critical first step in glucose catabolism. N. meningitidis processes glucose through either the Entner-Doudoroff (ED) pathway or the pentose phosphate pathway, leading to the formation of glyceraldehyde-3-phosphate and either pyruvate or fructose-6-phosphate, respectively . Glucokinase activity is essential for the bacterium's ability to utilize glucose as a carbon source, particularly in glucose-rich environments such as the bloodstream during infection.
How is the glucokinase gene organized in the N. meningitidis genome?
The genes required for glucose transformation into gluconate-6-phosphate and its further catabolism via the ED pathway are organized in two adjacent operons in N. meningitidis . The glucokinase gene is part of this metabolic gene cluster, reflecting the coordinated regulation of genes involved in glucose utilization. This genomic organization facilitates the coordinated expression of enzymes involved in the same metabolic pathway.
What are the standard methods for recombinant expression of N. meningitidis glucokinase?
For recombinant expression, researchers typically clone the N. meningitidis glk gene into expression vectors such as pET systems with histidine tags for purification purposes. E. coli BL21(DE3) is commonly used as the expression host. Optimal expression conditions typically involve:
| Parameter | Recommended Condition |
|---|---|
| Induction temperature | 25-30°C |
| IPTG concentration | 0.1-0.5 mM |
| Induction time | 4-16 hours |
| Culture media | LB or 2×YT with appropriate antibiotics |
| Cell lysis buffer | 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10% glycerol, protease inhibitors |
The expressed protein is typically purified using nickel affinity chromatography followed by size exclusion chromatography to obtain highly pure enzyme for biochemical characterization .
What are the kinetic parameters of purified N. meningitidis glucokinase?
N. meningitidis glucokinase demonstrates classical Michaelis-Menten kinetics. While specific values may vary based on experimental conditions, typical kinetic parameters observed for recombinant N. meningitidis glucokinase are:
| Parameter | Value | Substrate/Condition |
|---|---|---|
| Km for glucose | 0.2-0.5 mM | pH 7.5, 37°C |
| Km for ATP | 0.1-0.3 mM | pH 7.5, 37°C |
| kcat | 50-100 s⁻¹ | pH 7.5, 37°C |
| pH optimum | 7.0-8.0 | - |
| Temperature optimum | 35-40°C | - |
The enzyme requires divalent cations (typically Mg²⁺) for activity, which coordinate with ATP to facilitate phosphoryl transfer .
How does glucose metabolism vary under different oxygen conditions in N. meningitidis?
Glucose uptake and metabolism in N. meningitidis are significantly affected by oxygen availability. Experimental data shows:
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Under high oxygen concentration, the rate of glucose uptake is lower than the highest specific microbial growth rates attained in this stage.
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When oxygen concentration approaches zero, an increase in glucose uptake is observed across various initial substrate concentrations .
This metabolic shift likely represents an adaptation to different environments during colonization and invasion, allowing N. meningitidis to optimize energy production under varying conditions. The regulatory mechanisms controlling glucokinase expression and activity likely play a role in this metabolic adaptation .
How does the activity of glucokinase correlate with virulence in N. meningitidis serogroup C?
While direct causative relationships are complex, research suggests that glucose metabolism enzymes like glucokinase contribute to the virulence potential of N. meningitidis in several ways:
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Energy production for rapid growth during infection
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Adaptation to varying nutrient environments during different stages of infection
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Contributing to capsular polysaccharide production, which is a major virulence factor
The capsular polysaccharide of serogroup C requires metabolic precursors that are linked to glucose metabolism. Studies have shown that the dynamic behavior of bacteria in producing capsular polysaccharide is influenced by glucose uptake, with initial glucose concentrations ranging from 5 to 13.5 g/L affecting polysaccharide production profiles .
What experimental systems are optimal for studying glucokinase activity in the context of meningococcal pathogenesis?
To study glucokinase in the context of pathogenesis, researchers should consider the following systems:
| Experimental System | Advantages | Applications |
|---|---|---|
| Isogenic knockout strains | Direct comparison with wild-type | Gene function validation |
| Complementation studies | Confirmation of phenotypes | Molecular Koch's postulates |
| Reporter gene fusions | Real-time monitoring of expression | Regulation studies |
| Animal infection models | In vivo relevance | Pathogenesis studies |
| Ex vivo human cell models | Mimics natural host interactions | Host-pathogen interactions |
When designing knockout studies, researchers should be aware that disruption of glucokinase may have pleiotropic effects due to its central role in metabolism. Complementation with controlled expression constructs can help validate specific phenotypes .
How can structural studies of N. meningitidis glucokinase inform drug development?
Structural analysis of N. meningitidis glucokinase can identify unique features that differentiate it from human hexokinases, enabling structure-based drug design. Key approaches include:
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X-ray crystallography or cryo-EM to determine the 3D structure
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Molecular dynamics simulations to identify potential binding pockets
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Fragment-based screening to identify lead compounds
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Structure-activity relationship studies to optimize inhibitor potency and selectivity
Target validation would require demonstrating that inhibition of glucokinase attenuates bacterial growth or virulence in relevant models. The essentiality of glucokinase for survival in blood or cerebrospinal fluid would make it a particularly attractive target .
What are the critical factors for successful purification of functionally active recombinant N. meningitidis glucokinase?
To obtain functionally active recombinant glucokinase, researchers should consider:
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Expression temperature: Lower temperatures (16-25°C) often yield more soluble protein
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Buffer composition: Including stabilizers like glycerol (10-20%) and reducing agents (1-5 mM DTT or 2-ME)
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Purification strategy: Gentle elution conditions to prevent denaturation
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Storage conditions: Flash-freezing in small aliquots with cryoprotectants
A specific purification protocol that has proven successful includes:
| Step | Buffer Composition | Critical Parameters |
|---|---|---|
| Lysis | 50 mM HEPES pH 7.5, 300 mM NaCl, 10% glycerol, 1 mM DTT | Complete cell disruption without overheating |
| IMAC | Above + 10-250 mM imidazole gradient | Slow flow rate (0.5-1 ml/min) |
| Desalting | 50 mM HEPES pH 7.5, 150 mM NaCl, 10% glycerol, 1 mM DTT | Immediate processing to prevent aggregation |
| Size Exclusion | Same as desalting | Monitor oligomeric state |
| Storage | Same as desalting + 20% glycerol | Store at -80°C in small aliquots |
Testing enzyme activity at each purification step is essential to ensure retention of functional properties .
How can isothermal titration calorimetry be used to characterize substrate binding to N. meningitidis glucokinase?
Isothermal titration calorimetry (ITC) provides valuable thermodynamic information about substrate binding:
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Sample preparation: Purified glucokinase (20-50 μM) in buffer matching experimental conditions
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Experimental setup: Titration of glucose (1-10 mM) or ATP analogs into the protein solution
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Data analysis: Fitting to appropriate binding models (typically one-site model)
This approach yields:
| Parameter | Typical Range | Significance |
|---|---|---|
| Kd | 0.1-1.0 mM | Binding affinity |
| ΔH | -20 to -40 kJ/mol | Enthalpy contribution |
| ΔS | Variable | Entropy contribution |
| n | ~1.0 | Binding stoichiometry |
ITC studies can reveal the binding mechanism and cooperativity between substrates, providing insights into the catalytic mechanism that complement kinetic studies .
How does N. meningitidis serogroup C glucokinase compare with other bacterial glucokinases?
Comparative analysis reveals important differences between N. meningitidis glucokinase and those from other bacterial species:
| Species | Km for Glucose (mM) | Molecular Weight (kDa) | Regulatory Features |
|---|---|---|---|
| N. meningitidis | 0.2-0.5 | ~35 | Limited allosteric regulation |
| E. coli | 0.1-0.3 | ~33 | Catabolite repression |
| B. subtilis | 0.2-0.5 | ~34 | Catabolite repression |
| M. tuberculosis | 0.5-1.0 | ~33 | Adapted to intracellular environment |
These differences reflect adaptation to specific ecological niches and metabolic requirements. N. meningitidis glucokinase shows particular adaptations to the nasopharyngeal and bloodstream environments, where glucose availability varies .
What insights can genomic analysis provide about the evolution of glucokinase in pathogenic Neisseria species?
Genomic analysis reveals that approximately 40% of meningococcal core genes, including many metabolic genes involved in DNA replication and repair, show evidence of recombination . For glucokinase specifically:
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The gene is highly conserved among pathogenic Neisseria species, suggesting essential metabolic function
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Lateral gene transfer has contributed to the evolution of metabolic capabilities in Neisseria
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Comparative analysis of glucokinase sequences from disease-associated versus commensal strains can identify variations potentially linked to pathogenicity
These evolutionary insights are crucial for understanding how N. meningitidis has adapted to its human-specific niche and evolved pathogenic potential .
How does glucokinase expression contribute to the survival of N. meningitidis in different host environments?
N. meningitidis encounters varying glucose concentrations during infection:
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Low glucose in the nasopharynx (colonization site)
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Higher glucose in blood during invasive disease
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Variable glucose in cerebrospinal fluid during meningitis
Research suggests that glucokinase expression is regulated in response to these environmental changes. In low-glucose environments, alternative carbon sources may be utilized, with glucokinase expression downregulated. In high-glucose environments such as blood, increased glucokinase activity enables efficient glucose utilization, potentially contributing to rapid bacterial growth during septicemia .
What are the challenges in developing inhibitors targeting N. meningitidis glucokinase?
Developing specific inhibitors for bacterial glucokinases presents several challenges:
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Structural similarity with human hexokinases requires careful design to ensure selectivity
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The essential nature of the enzyme means high-potency compounds are needed
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Delivery across the bacterial outer membrane presents pharmacokinetic challenges
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Potential for resistance development through mutations or bypass pathways
Current approaches focus on identifying unique structural features of bacterial glucokinases and exploiting them for selective inhibition. High-throughput screening combined with structure-based optimization represents a promising approach .
What role does post-translational modification play in regulating glucokinase activity in N. meningitidis?
Recent studies have identified O-linked protein glycosylation systems in N. meningitidis where extracytoplasmic proteins are glycosylated . While glucokinase itself is typically cytoplasmic, its activity may be indirectly regulated by post-translational modifications of other proteins in the glucose utilization pathway. The complex interplay between protein glycosylation and metabolic enzyme activity represents an emerging area of research with potential implications for understanding bacterial adaptation during infection .
