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Minimal ATP-Independent N2-Reducing Systems Defined by L-Cluster-Bound Nitrogenase Assembly Platforms.

Robert Quechol1, Yimo Yang1, Chi Chung Lee1

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Angewandte Chemie (International Ed. in English)
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PubMed
Summary
This summary is machine-generated.

The L-cluster, an intermediate in nitrogenase assembly, endows proteins with nitrogen (N2) reducing activity. This finding suggests a simpler, ancestral nitrogenase and links nitrogen, carbon, and sulfur cycles.

Keywords:
ATP‐independent catalysisL‐clusterNifBNifENnitrogenase

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Area of Science:

  • Biochemistry
  • Bioinorganic Chemistry
  • Evolutionary Biology

Background:

  • Nitrogenase (NifH/NifDK) catalyzes N2 to NH3 conversion using the M-cluster metallocofactor.
  • M-cluster assembly involves NifB-mediated L-cluster formation and NifEN maturation.
  • The precise role of the L-cluster in nitrogenase assembly and function remains incompletely understood.

Purpose of the Study:

  • To investigate the intrinsic nitrogen (N2) reducing activity of the L-cluster and its associated proteins.
  • To explore the evolutionary implications of the L-cluster's reactivity for nitrogenase evolution.
  • To determine the role of the L-cluster in linking biogeochemical cycles.

Main Methods:

  • In vitro assays using L-cluster-bound NifB (NifBL) and NifEN (NifENL) with chemical reductants or photoexcited quantum dots.
  • In vivo N2 fixation experiments in NifH-deficient E. coli strains.
  • Bioinformatic analysis of L-cluster topology in ancient enzymes.

Main Results:

  • L-cluster-bound NifB and NifEN exhibit intrinsic ATP-independent N2 reduction activity.
  • N2 reduction capability is acquired by NifB only upon L-cluster formation.
  • In vivo N2 fixation is supported by NifBL and NifENL in NifH-deficient strains, with YfhL as the electron donor.

Conclusions:

  • The L-cluster possesses intrinsic N2-reducing activity, suggesting a simpler, one-component ancestral nitrogenase.
  • The L-cluster may represent an evolutionary link between nitrogen, carbon, and sulfur biogeochemical cycles.
  • This discovery reframes our understanding of nitrogen fixation evolution and the function of metalloenzymes.