20
Table 2.3 Known function of genes involved in N 2 fixation in A. vinelandii from Burén et al.
(2020) (https://pubs.acs.org/doi/full/10.1021/acs.chemrev.9b00489). Further permission must be
obtained from ACS. nifH, D, K, E, N and B have been proposed to be the minimal set of genes
required
Gene Proposed function
nifH
Fe protein. Obligate electron donor to the MoFe protein. Also required for FeMo-co
biosynthesis and apo-MoFe maturation (P-cluster maturation).
nifD
MoFe protein α-subunit. FeMo-co binding subunit. Forms an α 2 β 2 tetramer with NifK.
nifK
MoFe protein β-subunit. Forms an α2β2 tetramer with NifD.Dinitrogenase (MoFe
protein) (beta subunit)
nifT
Unknown
nifY
Interacts with apo-MoFe protein prior to FeMo-co insertion.
nafA
Unknown function.
nifE
Scaffold for NifB-co maturation into FeMo-co. Forms an α2β2 tetramer with NifN.
Scaffold for biosynthesis of dinitrogenase NifB cofactor maturation into FeMo-co
nifN
Scaffold for NifB-co maturation into FeMo-co. Forms an α2β2 tetramer with NifE.
Scaffold for biosynthesis of dinitrogenase NifB cofactor maturation into FeMo-co
nifX
Binds NifB-co and VK-cluster. Interacts with apo-NifEN. Proposed carrier of FeMo-co
precursors.
nafC
Unknown function.
feSII
Shethna protein II. Nitrogenase protection against O 2 .
nifIscA Fe − S scaffolding Nif protein. Contains a [4Fe-4S] cluster.
nifU
Supplies [Fe − S] clusters precursors for nitrogenase proteins and cofactors.
nifS
Mobilizes S for [Fe − S] cluster synthesis on NifU.
nifV
Homocitrate synthase. Involved in FeMo-co synthesis.
cysE1 Serine O-acetyltransferase. Participates in cysteine formation.
nafH Binds to apo-MoFe protein preceding P-cluster maturation.
nifW
Associates with apo-MoFe protein preceding P-cluster maturation.
nifZ
Involved in P-cluster maturation in combination with the Fe protein.
nifM
Essential for the maturation of the Fe protein. Proposed peptidyl-prolyl cis − trans
isomerases that would act over the Pro258 residue of NifH.
clpx2 Regulates NifEN and NifB protein levels.
nifF
Flavodoxin. Physiological electron donor to the Fe protein.
nifL
Sensor protein. Acts as NifA antiactivator.
nifA
Transcriptional activator. Forms a two-component regulatory system with NifL.
nifB
Ssential for FeMo-co synthesis. Catalyzes NifB-co formation, the first committed step
in FeMo-co biosynthesis.
fdxN
2x[4Fe-4S] ferredoxin. Required for NifB in the formation of NifB-co.
nifO
Required for simultaneous activation of nitrogenase and nitrate reductase.
nifQ
Processes Mo prior to its incorporation into FeMo-co.
nafW Rhodanase-like protein. Also called rhdN. Unknown function.
nafZ
Glutaredoxin-like protein. Also called grx5nif. Unknown function.
rnfA
Transmembrane protein. Part of the Rnf complex, which is involved in supplying low
potential electrons to the nitrogenase.
rnfB
Contains two [Fe − S] cluster binding sites. It is part of the Rnf complex.
rnfC
Contains [4Fe-4S] binding site. Electron transport component of the Rnf complex.
(continued)
2 Fundamentals of N 2 Fixation
Table 2.3 Known function of genes involved in N 2 fixation in A. vinelandii from Burén et al.
(2020) (https://pubs.acs.org/doi/full/10.1021/acs.chemrev.9b00489). Further permission must be
obtained from ACS. nifH, D, K, E, N and B have been proposed to be the minimal set of genes
required
Gene Proposed function
nifH
Fe protein. Obligate electron donor to the MoFe protein. Also required for FeMo-co
biosynthesis and apo-MoFe maturation (P-cluster maturation).
nifD
MoFe protein α-subunit. FeMo-co binding subunit. Forms an α 2 β 2 tetramer with NifK.
nifK
MoFe protein β-subunit. Forms an α2β2 tetramer with NifD.Dinitrogenase (MoFe
protein) (beta subunit)
nifT
Unknown
nifY
Interacts with apo-MoFe protein prior to FeMo-co insertion.
nafA
Unknown function.
nifE
Scaffold for NifB-co maturation into FeMo-co. Forms an α2β2 tetramer with NifN.
Scaffold for biosynthesis of dinitrogenase NifB cofactor maturation into FeMo-co
nifN
Scaffold for NifB-co maturation into FeMo-co. Forms an α2β2 tetramer with NifE.
Scaffold for biosynthesis of dinitrogenase NifB cofactor maturation into FeMo-co
nifX
Binds NifB-co and VK-cluster. Interacts with apo-NifEN. Proposed carrier of FeMo-co
precursors.
nafC
Unknown function.
feSII
Shethna protein II. Nitrogenase protection against O 2 .
nifIscA Fe − S scaffolding Nif protein. Contains a [4Fe-4S] cluster.
nifU
Supplies [Fe − S] clusters precursors for nitrogenase proteins and cofactors.
nifS
Mobilizes S for [Fe − S] cluster synthesis on NifU.
nifV
Homocitrate synthase. Involved in FeMo-co synthesis.
cysE1 Serine O-acetyltransferase. Participates in cysteine formation.
nafH Binds to apo-MoFe protein preceding P-cluster maturation.
nifW
Associates with apo-MoFe protein preceding P-cluster maturation.
nifZ
Involved in P-cluster maturation in combination with the Fe protein.
nifM
Essential for the maturation of the Fe protein. Proposed peptidyl-prolyl cis − trans
isomerases that would act over the Pro258 residue of NifH.
clpx2 Regulates NifEN and NifB protein levels.
nifF
Flavodoxin. Physiological electron donor to the Fe protein.
nifL
Sensor protein. Acts as NifA antiactivator.
nifA
Transcriptional activator. Forms a two-component regulatory system with NifL.
nifB
Ssential for FeMo-co synthesis. Catalyzes NifB-co formation, the first committed step
in FeMo-co biosynthesis.
fdxN
2x[4Fe-4S] ferredoxin. Required for NifB in the formation of NifB-co.
nifO
Required for simultaneous activation of nitrogenase and nitrate reductase.
nifQ
Processes Mo prior to its incorporation into FeMo-co.
nafW Rhodanase-like protein. Also called rhdN. Unknown function.
nafZ
Glutaredoxin-like protein. Also called grx5nif. Unknown function.
rnfA
Transmembrane protein. Part of the Rnf complex, which is involved in supplying low
potential electrons to the nitrogenase.
rnfB
Contains two [Fe − S] cluster binding sites. It is part of the Rnf complex.
rnfC
Contains [4Fe-4S] binding site. Electron transport component of the Rnf complex.
(continued)
2 Fundamentals of N 2 Fixation