The catalytic subunit of Escherichia coli nitrate reductase A contains a novel [4Fe-4S] cluster with a high-spin ground stateRothery, R.A., Bertero, M.G., Cammack, R., Palak, M., Blasco, F., Strynadka, N.C., Weiner, J.H.
(2004) Biochemistry 43: 5324-5333
- PubMed: 15122898
- DOI: 10.1021/bi049938l
- PubMed Abstract:
- Insights Into the Respiratory Electron Transfer Pathway from the Structure of Nitrate Reductase A
Bertero, M.G.,Rothery, R.A.,Palak, M.,Hou, C.,Lim, D.,Blasco, F.,Weiner, J.H.,Strynadka, N.C.J.
(2003) Nat.Struct.Mol.Biol. 10: 681
We have used EPR spectroscopy, redox potentiometry, and protein crystallography to characterize the [4Fe-4S] cluster (FS0) of the Escherichia coli nitrate reductase A (NarGHI) catalytic subunit (NarG). FS0 is clearly visible in the crystal structure ...
We have used EPR spectroscopy, redox potentiometry, and protein crystallography to characterize the [4Fe-4S] cluster (FS0) of the Escherichia coli nitrate reductase A (NarGHI) catalytic subunit (NarG). FS0 is clearly visible in the crystal structure of NarGHI [Bertero, M. G., et al. (2003) Nat. Struct. Biol. 10, 681-687] but has novel coordination comprising one His residue and three Cys residues. At low temperatures (<15 K), reduced NarGHI exhibits a previously unobserved EPR signal comprising peaks at g = 5.023 and g = 5.556. We have assigned these features to a [4Fe-4S](+) cluster with an S = (3)/(2) ground state, with the g = 5.023 and g = 5.556 peaks corresponding to subpopulations exhibiting DeltaS = (1)/(2) and DeltaS = (3)/(2) transitions, respectively. Both peaks exhibit midpoint potentials of approximately -55 mV at pH 8.0 and are eliminated in the EPR spectrum of apomolybdo-NarGHI. The structure of apomolybdo-NarGHI reveals that FS0 is still present but that there is significant conformational disorder in a segment of residues that includes one of the Cys ligands. On the basis of these observations, we have assigned the high-spin EPR features of reduced NarGHI to FS0.
CIHR Membrane Protein Research Group, Department of Biochemistry, University of Alberta, 474 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada.