One- and Two-Dimensional Proton NMR Studies of the Active Site of Iron(II) Superoxide Dismutase from Escherichia coli

Authors

Li-June Ming, University of South Florida
John B. Lynch, University of Minnesota - Twin Cities
Richard C. Holz, Marquette UniversityFollow
Lawrence Que Jr., University of Minnesota - Twin CitiesFollow

Document Type

Article

Publication Date

1-1-1994

Source Publication

Inorganic Chemistry

Source ISSN

0020-1669

Abstract

The iron(II) superoxide dismutase (FeSOD) from Escherichia coli exhibits relatively sharp well-resolved paramagnetically shifted NMR signals. These signals can be associated with the endogenous ligands characterized by X-ray crystallography for the oxidized form Fe^IlISOD. Our results demonstrate that the active site remains intact upon reduction of the Fe(III) site, retaining the same coordination modes for the three N,-coordinated His residues (presumably His-26, His-75, and His-162) and the Asp residue (presumably Asp-158). The N-H resonances of the coordinated histidines are found at 88, 43, and 37 ppm, while the signals at 24.5 (E), 19 (G), and 15 (J) ppm are assigned to the Asp residue by the observation of nuclear Overhauser effects (NOB) and bond correlations among the resonances. Distances of 1.9 and 2.4 Å can be estimated between the protons Band G and the protons Band J, respectively, attributable to the -C_βH₂-C_αH < spin system of the Asp residue. The Asp assignments are corroborated by the observation of interresidue interactions between the C_αH's of Asp-158 and Trp-160. The resonances of the latter residue are identified by NOB and scalar connectivities, the most critical assignment being the N_αH at 22 ppm (F). According to the crystal structure of the corresponding enzyme from Psedumonas ovalis (Stoddard, B. L.; Howell, P. L.; Ringe, D.; Petsko, G. A. Biochemistry 1990, 29, 8885-8893), this proton is hydrogen-bonded to the free carboxylate oxygen of Asp-158. This interaction thus rationalizes the paramagnetic shift observed for signal F and its very slow exchange with solvent which occurs only upon long-term standing.

Comments

Inorganic Chemistry, Vol. 33, No. 1 (January 1, 1994): 83-87. DOI.

Richard C. Holz was affiliated with University of Minnesota at the time of publication.

Recommended Citation

Ming, Li-June; Lynch, John B.; Holz, Richard C.; and Que, Lawrence Jr., "One- and Two-Dimensional Proton NMR Studies of the Active Site of Iron(II) Superoxide Dismutase from Escherichia coli" (1994). Chemistry Faculty Research and Publications. 320.
https://epublications.marquette.edu/chem_fac/320