Swapping metals in Fe- and Mn-dependent dioxygenases: Evidence for oxygen activation without a change in metal redox state
Year: 2008
Type: article
Abstract: Biological O(2) activation often occurs after binding to a reduced metal [e.g., M(II)] in an enzyme active site. Subsequent M(II)-to-O(2) electron transfer results in a reactive M(III)-superoxo species. For the extradiol aromatic ring-cleaving dioxygenases, we have proposed a different model where an electron is transferred from substrate to O(2) via the M(II) center to which they are both bound, thereby obviating the need for an integral change in metal redox state. This model is tested by using homoprotocatechuate 2,3-dioxygenases from Brevibacterium fuscum (Fe-HPCD) and Arthrobacter globiformis (Mn-MndD) that share high sequence identity and very similar structures. Despite these similarities, Fe-HPCD binds Fe(II) whereas Mn-MndD incorporates Mn(II). Methods are described to incorporate the nonphysiological metal into each enzyme (Mn-HPCD and Fe-MndD). The x-ray crystal structure of Mn-HPCD at 1.7 A is found to be indistinguishable from that of Fe-HPCD, while EPR studies show that the Mn(II) sites of Mn-MndD and Mn-HPCD, and the Fe(II) sites of the NO complexes of Fe-HPCD and Fe-MndD, are very similar. The uniform metal site structures of these enzymes suggest that extradiol dioxygenases cannot differentially compensate for the 0.7-V gap in the redox potentials of free iron and manganese. Nonetheless, all four enzymes exhibit nearly the same K(M) and V(max) values. These enzymes constitute an unusual pair of metallo-oxygenases that remain fully active after a metal swap, implicating a different way by which metals are used to promote oxygen activation without an integral change in metal redox state.
Institution: University of Minnesota
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: bronze
Awards: G102163711, G1055550527, G107546177, G1313983767, G1664757510, G1805209620, G1822506642, G1841091238, G220149836, G262962599, G2784524989, G2857925935, G3075337988, OXYGENASE ENZYME MECHANISM, NON-HEME IRON OXYGEN ACTIVATION IN ENZYME AND MODELS, G5607048534, G6848031779, Intermediates in O2 Activation by Oxygenases, G7552424089, Chemistry-Biology Interface Training Grant, NONHEME IRON DIOXYGEN ACTIVATION IN ENZYMES AND MODELS, Redox Chemistry of 2His-1 Carboxylate Metalloenzymes, G969889393
OpenAlex ID: W2111969713