1siw: Difference between revisions

[[Image:1siw.gif|left|200px]]<br /><applet load="1siw" size="350" color="white" frame="true" align="right" spinBox="true"  

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 (&lt;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.

1SIW is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=GDP:'>GDP</scene>, <scene name='pdbligand=HEM:'>HEM</scene>, <scene name='pdbligand=SF4:'>SF4</scene>, <scene name='pdbligand=F3S:'>F3S</scene> and <scene name='pdbligand=3PH:'>3PH</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Nitrate_reductase Nitrate reductase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.7.99.4 1.7.99.4] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1SIW OCA].  

[[Category: Bertero, M G.]]

[[Category: Rothery, R A.]]

[[Category: Strynadka, N C.]]

[[Category: Weiner, J H.]]

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