Cobalt tetradehydrocorrins coordinated by imidazolate-like histidine in the heme pocket of horseradish peroxidase

  • Koji Oohora
  • Ning Tang
  • Yoshitsugu Morita
  • Takashi Hayashi
Original Paper

DOI: 10.1007/s00775-017-1458-z

Cite this article as:
Oohora, K., Tang, N., Morita, Y. et al. J Biol Inorg Chem (2017). doi:10.1007/s00775-017-1458-z
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Part of the following topical collections:
  1. AsBIC8: 8th Asian Biological Inorganic Chemistry Special Issue

Abstract

Horseradish peroxidase was reconstituted with cobalt tetradehydrocorrin, rHRP(Co(TDHC)), as a structural analog of cobalamin coordinated with an imidazolate-like His residue, which is generally seen in native enzymes. In contrast to the previously reported cobalt tetradehydrocorrin-reconstituted myoglobin, rMb(Co(TDHC)), the HRP matrix was expected to provide strong axial ligation by His170 which has imidazolate character. rHRP(CoII(TDHC)) was characterized by EPR and its reaction with reductants indicates a negative shift of its redox potential compared to rMb(Co(TDHC)). Furthermore, aqua- and CN-forms of Co(III) state were prepared. The former species was obtained by oxidation of rHRP(CoII(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter was prepared by ligand exchange of rHRP(CoIII(OH)(TDHC)) with exogenous cyanide upon addition of KCN. The 13C NMR chemical shift of cyanide in rHRP(CoIII(CN)(TDHC)) was determined to be 121.8 ppm. IR measurements show that the cyanide of rHRP(CoIII(CN)(TDHC)) has a stretching frequency peak at 2144 cm−1. The 13C NMR and IR measurements indicate strong coordination of cyanide to CoIII(TDHC) relative to rMb(CoIII(CN)(TDHC)). Thus, the extent of π-back donation from the cobalt ion to the cyanide ion is relatively high in rHRP(CoIII(CN)(TDHC)). The pK1/2 values of rHRP(CoIII(OH)(TDHC)) and rHRP(CoIII(CN)(TDHC)) are the same (pK1/2 = 3.2) as determined by a pH titration experiment, indicating that cyanide ligation does not affect Co–His ligation, whereas cyanide ligation weakens the Co–His ligation in rMb(CoIII(CN)(TDHC)). Taken together, these results indicate that HRP reconstituted with cobalt tetradehydrocorrin is a suitable cobalamin-dependent enzyme model with imidazolate-like His residue.

Keywords

Cofactor Cobalamin model Cobalt tetradehydrocorrin Ligand binding 

Supplementary material

775_2017_1458_MOESM1_ESM.pdf (544 kb)
Supplementary material 1 (PDF 543 kb)

Copyright information

© SBIC 2017

Authors and Affiliations

  • Koji Oohora
    • 1
    • 2
  • Ning Tang
    • 1
  • Yoshitsugu Morita
    • 1
    • 3
    • 4
  • Takashi Hayashi
    • 1
  1. 1.Department of Applied Chemistry, Graduate School of EngineeringOsaka UniversitySuitaJapan
  2. 2.PRESTO JSTKawaguchiJapan
  3. 3.Institute for Materials Chemistry and Engineering and International Research Center for Molecular SystemsKyushu UniversityFukuokaJapan
  4. 4.Faculty of Science and Engineering, Department of Applied ChemistryChuo UniversityBunkyo-kuJapan

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