1kf6

[[Image:1kf6.gif|left|200px]]<br /><applet load="1kf6" size="450" color="white" frame="true" align="right" spinBox="true"

==Overview==

The quinol-fumarate reductase (QFR) respiratory complex of Escherichia, coli is a four-subunit integral-membrane complex that catalyzes the final, step of anaerobic respiration when fumarate is the terminal electron, acceptor. The membrane-soluble redox-active molecule menaquinol (MQH(2)), transfers electrons to QFR by binding directly to the membrane-spanning, region. The crystal structure of QFR contains two quinone species, presumably MQH(2), bound to the transmembrane-spanning region. The binding, sites for the two quinone molecules are termed Q(P) and Q(D), indicating, their positions proximal (Q(P)) or distal (Q(D)) to the site of fumarate, reduction in the hydrophilic flavoprotein and iron-sulfur protein, subunits. It has not been established whether both of these sites are, mechanistically significant. Co-crystallization studies of the E. coli QFR, with the known quinol-binding site inhibitors, 2-heptyl-4-hydroxyquinoline-N-oxide and 2-[1-(p-chlorophenyl)ethyl], 4,6-dinitrophenol establish that both inhibitors block the binding of, MQH(2) at the Q(P) site. In the structures with the inhibitor bound at, Q(P), no density is observed at Q(D), which suggests that the occupancy of, this site can vary and argues against a structurally obligatory role for, quinol binding to Q(D). A comparison of the Q(P) site of the E. coli, enzyme with quinone-binding sites in other respiratory enzymes shows that, an acidic residue is structurally conserved. This acidic residue, Glu-C29, in the E. coli enzyme may act as a proton shuttle from the quinol during, enzyme turnover.

1KF6 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 K, OAA, ACT, FES, F3S, SF4, FAD, HQO, CE1 and 1PE as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Succinate_dehydrogenase Succinate dehydrogenase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.3.99.1 1.3.99.1] Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1KF6 OCA].

 

[[Category: Croal, L.R.]]

[[Category: Iverson, T.M.]]

[[Category: Rees, D.C.]]

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