Recombinant Nitratiruptor sp. GMP synthase [glutamine-hydrolyzing] (guaA), partial
Description
Biochemical Function and Catalytic Mechanism
GMP synthase (guaA) catalyzes the ATP-dependent amination of xanthosine monophosphate (XMP) to form guanosine monophosphate (GMP), utilizing glutamine as a nitrogen donor. This reaction occurs via two distinct active sites:
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Glutaminase domain: Hydrolyzes glutamine to generate ammonia.
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ATPPase domain: Activates XMP through adenylation (forming AMP-XMP) and incorporates ammonia to produce GMP .
The enzyme’s partial recombinant form retains catalytic activity but lacks full-length structural domains, often requiring optimization for stability and function .
Production and Purification
Recombinant guaA is typically expressed in E. coli systems, as exemplified by related species:
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Expression Vector: pET or pBSV2G plasmids with antibiotic resistance markers .
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Tags: Affinity tags (e.g., His-tag) for purification, though exact tags vary by construct .
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Storage: -20°C for short-term; -80°C for long-term stability .
Kinetic and Biochemical Properties
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Substrate Specificity: Binds XMP, ATP, and glutamine with micromolar affinity .
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Allosteric Regulation: ATP/Mg²⁺ and XMP activate glutaminase activity up to 10-fold .
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Ammonia Channeling: Prevents NH₃ equilibration with the external medium, enhancing efficiency .
Mutational Studies
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Cys-to-Ala Mutants: Abolish glutaminase activity but retain ATPPase function .
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Domain Deletions: Partial constructs (e.g., 1–525 aa) maintain adenylation activity but require exogenous ammonia .
Applications and Research Implications
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Antimicrobial Targets: Essential for pathogens like Borrelia burgdorferi and Clostridioides difficile, making guaA a drug candidate .
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Biochemical Tools: Used to study purine metabolism and allosteric regulation mechanisms .
Challenges and Limitations
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Instability: Repeated freeze-thaw cycles degrade partial constructs .
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Species-Specific Variations: Archaeal vs. bacterial guaA differ in domain architecture (single vs. two-subunit types) .
Comparative Analysis of Recombinant guaA Constructs
Product Specs
Target Background
KEGG: nis:NIS_1339
STRING: 387092.NIS_1339
