Crystal Structures and Coordination Behavior of Aqua- and Cyano-Co(III) Tetradehydrocorrins in the Heme Pocket of Myoglobin

Yoshitsugu Morita, Koji Oohora, Eiichi Mizohata, Akiyoshi Sawada, Takashi Kamachi, Kazunari Yoshizawa, Tsuyoshi Inoue, Takashi Hayashi

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Abstract

Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(CoII(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(CoIII(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(CoIII(OH)(TDHC)) and rMb(CoIII(CN)(TDHC)) at 1.20 and 1.40 Å resolution, respectively. The 13C NMR chemical shifts of the cyanide in rMb(CoIII(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(CoIII(CN)(TDHC)) has a stretching frequency peak at 2151 cm-1 which is higher than that of cyanocobalamin. The 13C NMR and IR measurements indicate weaker coordination of the cyanide to CoIII(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of π-back-donation from the cobalt ion to the cyanide ion is lower in rMb(CoIII(CN)(TDHC)). Furthermore, the pK1/2 values of rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(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.

Original languageEnglish
Pages (from-to)1287-1295
Number of pages9
JournalInorganic Chemistry
Volume55
Issue number3
DOIs
Publication statusPublished - Feb 1 2016

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myoglobin
Myoglobin
Cyanides
cyanides
Heme
Crystal structure
crystal structure
Vitamin B 12
cyanocobalamin
Nuclear magnetic resonance
5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase
Ions
Ligands
proteins
vitamins
methionine
nuclear magnetic resonance
ligands
Chemical shift
Cobalt

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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Crystal Structures and Coordination Behavior of Aqua- and Cyano-Co(III) Tetradehydrocorrins in the Heme Pocket of Myoglobin. / Morita, Yoshitsugu; Oohora, Koji; Mizohata, Eiichi; Sawada, Akiyoshi; Kamachi, Takashi; Yoshizawa, Kazunari; Inoue, Tsuyoshi; Hayashi, Takashi.

In: Inorganic Chemistry, Vol. 55, No. 3, 01.02.2016, p. 1287-1295.

Research output: Contribution to journalArticle

Morita, Yoshitsugu ; Oohora, Koji ; Mizohata, Eiichi ; Sawada, Akiyoshi ; Kamachi, Takashi ; Yoshizawa, Kazunari ; Inoue, Tsuyoshi ; Hayashi, Takashi. / Crystal Structures and Coordination Behavior of Aqua- and Cyano-Co(III) Tetradehydrocorrins in the Heme Pocket of Myoglobin. In: Inorganic Chemistry. 2016 ; Vol. 55, No. 3. pp. 1287-1295.
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abstract = "Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(CoII(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(CoIII(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(CoIII(OH)(TDHC)) and rMb(CoIII(CN)(TDHC)) at 1.20 and 1.40 {\AA} resolution, respectively. The 13C NMR chemical shifts of the cyanide in rMb(CoIII(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(CoIII(CN)(TDHC)) has a stretching frequency peak at 2151 cm-1 which is higher than that of cyanocobalamin. The 13C NMR and IR measurements indicate weaker coordination of the cyanide to CoIII(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of π-back-donation from the cobalt ion to the cyanide ion is lower in rMb(CoIII(CN)(TDHC)). Furthermore, the pK1/2 values of rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(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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T1 - Crystal Structures and Coordination Behavior of Aqua- and Cyano-Co(III) Tetradehydrocorrins in the Heme Pocket of Myoglobin

AU - Morita, Yoshitsugu

AU - Oohora, Koji

AU - Mizohata, Eiichi

AU - Sawada, Akiyoshi

AU - Kamachi, Takashi

AU - Yoshizawa, Kazunari

AU - Inoue, Tsuyoshi

AU - Hayashi, Takashi

PY - 2016/2/1

Y1 - 2016/2/1

N2 - Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(CoII(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(CoIII(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(CoIII(OH)(TDHC)) and rMb(CoIII(CN)(TDHC)) at 1.20 and 1.40 Å resolution, respectively. The 13C NMR chemical shifts of the cyanide in rMb(CoIII(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(CoIII(CN)(TDHC)) has a stretching frequency peak at 2151 cm-1 which is higher than that of cyanocobalamin. The 13C NMR and IR measurements indicate weaker coordination of the cyanide to CoIII(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of π-back-donation from the cobalt ion to the cyanide ion is lower in rMb(CoIII(CN)(TDHC)). Furthermore, the pK1/2 values of rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(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.

AB - Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(CoII(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(CoIII(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(CoIII(OH)(TDHC)) and rMb(CoIII(CN)(TDHC)) at 1.20 and 1.40 Å resolution, respectively. The 13C NMR chemical shifts of the cyanide in rMb(CoIII(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(CoIII(CN)(TDHC)) has a stretching frequency peak at 2151 cm-1 which is higher than that of cyanocobalamin. The 13C NMR and IR measurements indicate weaker coordination of the cyanide to CoIII(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of π-back-donation from the cobalt ion to the cyanide ion is lower in rMb(CoIII(CN)(TDHC)). Furthermore, the pK1/2 values of rMb(CoIII(OH2)(TDHC)) and rMb(CoIII(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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