Evidence of Histidine Coordination to the Catalytic Ferrous Ion in the Ring-Cleavlng 2,2′,3-Trihydroxybiphenyl Dioxygenase from the Dibenzofuran-Degrading Bacterium Sphingomonas sp Strain RW1

Abstract

The 1H NMR spectra of an aromatic ring-cleaving extradiol dioxygenase, 2,2′,3-trihydroxybiphenyl dioxygenase of the dibenzofuran-degrading bacterium Sphingomonas sp. strain RW1, are reported. In the catalytically active reduced form of the monomeric enzyme (MW=32 kDa), three broad strongly downfield shifted signals were observed, two of which disappeared in D 2O solution. Their shifts and linewidths are consistent with ring NH and meta-like protons of coordinated histidines. These signals show strong sensitivity to the presence of the substrate. The oxidized form of the enzyme shows no hyperfine shifted signals. It is suggested that the high spin Fe(II) ion present in the active form of the enzyme is coordinated by at least two histidines. This is the first report of hyperfine shifted NMR signals being detected for an extradiol dioxygenase.