5azr: Difference between revisions

<StructureSection load='5azr' size='340' side='right' caption='[[5azr]], [[Resolution|resolution]] 1.20&Aring;' scene=''>

<table><tr><td colspan='2'>[[5azr]] is a 1 chain structure with sequence from [http://en.wikipedia.org/wiki/Equus_caballus Equus caballus]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=5AZR OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=5AZR FirstGlance]. <br>

</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat"><scene name='pdbligand=GOL:GLYCEROL'>GOL</scene>, <scene name='pdbligand=J1R:(1R,19R)+COBALT+TETRADEHYDROCORRIN'>J1R</scene>, <scene name='pdbligand=J1S:(1S,19S)+COBALT+TETRADEHYDROCORRIN'>J1S</scene>, <scene name='pdbligand=SO4:SULFATE+ION'>SO4</scene></td></tr>

<tr id='related'><td class="sblockLbl"><b>[[Related_structure|Related:]]</b></td><td class="sblockDat">[[5azq|5azq]]</td></tr>

<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=5azr FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=5azr OCA], [http://pdbe.org/5azr PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=5azr RCSB], [http://www.ebi.ac.uk/pdbsum/5azr PDBsum]</span></td></tr>

[[http://www.uniprot.org/uniprot/MYG_HORSE MYG_HORSE]] Serves as a reserve supply of oxygen and facilitates the movement of oxygen within muscles.

Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(Co(III)(OH2)(TDHC)) and rMb(Co(III)(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(Co(II)(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(Co(III)(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(Co(III)(OH)(TDHC)) and rMb(Co(III)(CN)(TDHC)) at 1.20 and 1.40 A resolution, respectively. The (13)C NMR chemical shifts of the cyanide in rMb(Co(III)(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(Co(III)(CN)(TDHC)) has a stretching frequency peak at 2151 cm(-1) which is higher than that of cyanocobalamin. The (13)C NMR and IR measurements indicate weaker coordination of the cyanide to Co(III)(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of pi-back-donation from the cobalt ion to the cyanide ion is lower in rMb(Co(III)(CN)(TDHC)). Furthermore, the pK1/2 values of rMb(Co(III)(OH2)(TDHC)) and rMb(Co(III)(CN)(TDHC)) were determined by a pH titration experiment to be 3.2 and 5.5, respectively, indicating that the cyanide ligation weakens the Co-N(His93) bond. Theoretical calculations also demonstrate that the axial ligand exchange from water to cyanide elongates the Co-N(axial) bond with a decrease in the bond dissociation energy. Taken together, the cyano-Co(III) tetradehydrocorrin in myoglobin is appropriate for investigation as a structural analogue of methylcobalamin, a key intermediate in methionine synthase reaction.

 

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== References ==

[[Category: Hayashi, T]]

[[Category: Inoue, T]]

[[Category: Mizohata, E]]

[[Category: Morita, Y]]

[[Category: Oohora, K]]

[[Category: Redox protein]]