Coordination of a histidine residue of the protein‐component S to the cobalt atom in coenzyme B12‐dependent glutamate mutase from Clostridium cochlearium

FEBS Letters

Zelder, Oskar¹  Beatrix, Birgitta¹  Buckel, Wolfgang¹  Kroll, Friedrich¹ 

[1] Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Karl-v.-Frisch-Str., D-35032 Marburg, Germany

关键词: Coenzyme B12;    Glutamate mutase;    Clostridium cochlearium;    Electron paramagnetic resonance;    [15N]Histidine;   

DOI  :  10.1016/0014-5793(95)00762-X

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Electron paramagnetic resonance (EPR) spectroscopy of glutamate mutase from Clostridium cochlearium was performed in order to test the idea, that a histidine residue of component S replaces the dimethylbenzimidazole ligand of the Co-atom during binding of coenzyme B₁₂ to the enzyme. The shapes and the superhyperfine splitting of the g _z-lines of the Co(II) EPR spectra were used as indicators of the interaction of the axial base nitrogen with the Co-atom. A mixture of completely ¹⁵N-labelled component S, unlabelled component E, coenzyme B₁₂ and glutamate gave slightly sharper g _z-lines than that with unlabelled component S. A more dramatic change was observed in the Co(II) spectrum of the inactivated enzyme containing tightly bound cob(II)alamin, in which unlabelled component S caused a threefold superhyperfine-splitting of the g _z-line, whereas the ¹⁵N-labelled protein only caused a twofold splitting, as expected for a direct interaction of a nitrogen of the enzyme with the Co-atom. By using a sample of ¹⁵N-labelled component S, in which only the histidines were ¹⁴N-labelled, the EPR spectra showed no difference to those with unlabelled component S. The experiments indeed demonstrate a replacement of the dimethylbenzimidazole ligand in coenzyme B₁₂ by a histidine when bound to glutamate mutase. The most likely candidate is H16, which is conserved among the carbon skeleton rearranging mutases and methionine synthase.

【 授权许可】

Unknown