Premium
Coordination of a histidine residue of the protein‐component S to the cobalt atom in coenzyme B 12 ‐dependent glutamate mutase from Clostridium cochlearium
Author(s) -
Zelder Oskar,
Beatrix Birgitta,
Kroll Friedrich,
Buckel Wolfgang
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00762-x
Subject(s) - histidine , cobalt , chemistry , residue (chemistry) , cofactor , component (thermodynamics) , mutase , biochemistry , stereochemistry , amino acid , inorganic chemistry , enzyme , physics , thermodynamics
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 B 12 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 15 N‐labelled component S, unlabelled component E, coenzyme B 12 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 15 N‐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 15 N‐labelled component S, in which only the histidines were 14 N‐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 B 12 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.