Thu, 24 Jul 2008 20:28:13 BST CiteULike: neils Hajdu http://www.citeulike.org/user/neils/author/Hajdu CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/neils/article/2783973 <i>Journal of molecular biology, Vol. 269, No. 3. (13 June 1997), pp. 440-455.</i><br /><br />The central tunnel of the eight-bladed beta-propeller domain of cytochrome cd1 (nitrite reductase) is seen, from a 1.28 A resolution structure, to contain hydrogen donors and acceptors that are satisfied by interaction either with water or the d1 haem. The d1 haem, although bound by an extensive network of hydrogen bonds, is not distorted in its binding pocket and is confirmed to have exactly the dioxoisobacteriochlorin structure proposed from chemical studies. A biological rationale is advanced for the undistorted structure of the d1 haem and the large number of hydrogen bonds it makes. The beta-propeller domain can be closely superimposed on that of methanol dehydrogenase despite the enzymes sharing no common sequence motifs and using a different set of interactions to "Velcro" close the propeller. The sequence and likely structural relationships between cytochrome cd1 or methanol dehydrogenase and other predicted eight-bladed beta-propeller domains in proteins, such as the pyrolloquinoline quinone-dependent alcohol dehydrogenase, are discussed and compared with other propeller proteins. From sequencing the nirS gene of Thiosphaera pantotropha, it is established that the amino acid sequence deduced previously in part from X-ray diffraction data at lower resolution was largely correct, as was the proposal that eight N-terminal amino acid residues were not seen in the structure. The unusual haem iron environments in both the c-type cytochrome domain, with His/His coordination, and the d1-type cytochrome domain with Tyr/His coordination are related to the functions of the redox centres. Cytochrome cd1 structure: unusual haem environments in a nitrite reductase and analysis of factors contributing to beta-propeller folds. SC Baker NF Saunders AC Willis SJ Ferguson J Hajdu V Fülöp doi:10.1006/jmbi.1997.1070 Journal of molecular biology, Vol. 269, No. 3. (13 June 1997), pp. 440-455. 2008-05-11T09:19:15-00:00 1997 Journal of molecular biology 0022-2836 269 3 440 455 beta-propeller cytochrome haem nitrite protein reductase structure http://www.citeulike.org/user/neils/article/2783970 <i>Nature, Vol. 389, No. 6649. (25 September 1997), pp. 406-412.</i><br /><br />Cytochrome cd1 nitrite reductase catalyses the conversion of nitrite to nitric oxide in the nitrogen cycle. The crystal structure of the oxidized enzyme shows that the d1 haem iron of the active site is ligated by His/Tyr side chains, and the c haem iron is ligated by a His/His ligand pair. Here we show that both haems undergo re-ligation during catalysis. Upon reduction, the tyrosine ligand of the d1 haem is released to allow substrate binding. Concomitantly, a refolding of the cytochrome c domain takes place, resulting in an unexpected change of the c haem iron coordination from His 17/His 69 to Met106/His69. This step is similar to the last steps in the folding of cytochrome c. The changes must affect the redox potential of the haems, and suggest a mechanism by which internal electron transfer is regulated. Structures of reaction intermediates show how nitric oxide is formed and expelled from the active-site iron, as well as how both haems return to their starting coordination. These results show how redox energy can be switched into conformational energy within a haem protein. Haem-ligand switching during catalysis in crystals of a nitrogen-cycle enzyme. PA Williams V Fülöp EF Garman NF Saunders SJ Ferguson J Hajdu doi:10.1038/38775 Nature, Vol. 389, No. 6649. (25 September 1997), pp. 406-412. 2008-05-11T09:17:32-00:00 1997 Nature 0028-0836 389 6649 406 412 crystallography haem mechanism nitrite protein reductase structure