Recombinant Respiratory nitrate reductase alpha chain (narG), partial
Description
Introduction
The recombinant respiratory nitrate reductase alpha chain (narG) is a critical component of bacterial nitrate reductase complexes, enabling nitrate reduction in anaerobic environments. This enzyme is part of the NarGHI complex in E. coli and related species, where it catalyzes the reduction of nitrate (NO₃⁻) to nitrite (NO₂⁻) using quinol as an electron donor . The "partial" designation refers to engineered truncations or fragments used in biochemical studies, often to isolate functional domains .
Functional Role in Nitrate Metabolism
NarG is essential for initiating denitrification, converting nitrate to nitrite under anaerobic conditions. Its activity is tightly regulated:
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Induction: Expressed during anaerobic respiration on nitrate (ARN), mediated by the NarXL transcription factor .
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NO production: NarGHI generates nitric oxide (NO), which S-nitrosylates proteins like OxyR, modulating oxidative stress responses .
Interactions with Denitrification Machinery
NarG interacts with downstream enzymes to form a functional denitrification network:
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NorBC: NarG binds NorB and NorC, linking nitrate reduction to nitric oxide reductase activity .
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NirS: NarG expression stabilizes the nitrite reductase NirS via protein-protein interactions .
Gene Disruption Studies
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P. fluorescens: Deletion of narG abolished nitrate reductase activity, delaying anaerobic growth with nitrite .
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S. aureus: narGHJI disruption reduced NO production and virulence gene expression (agr system) .
Environmental Relevance
narG genes are prevalent in estuarine sediments, with sequences diverging from cultured isolates, highlighting their ecological significance in nitrogen cycling .
