Crystal Structures of ModA from Escherichia coli and Formaldehyde Ferredoxin Oxidoreductase from Pyrococcus furiosus

Citation

Hu, Yonglin (1999) Crystal Structures of ModA from Escherichia coli and Formaldehyde Ferredoxin Oxidoreductase from Pyrococcus furiosus. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/j04r-6905. https://resolver.caltech.edu/CaltechTHESIS:07312025-184818403

Abstract

The crystal structures of two proteins, ModA from Escherichia coli and formaldehyde ferredoxin oxidoreductase from Pyrococcus furiosus, are reported in this paper.

ModA is a periplasmic molybdate binding protein. Crystals of this protein complexed with tungstate or molybdate belong to space groups P3₂21, with cell dimensions of a=b=82.6Ź, c=81.5Å, α=β=90°, and γ=120°. The structure of ModA was solved by the Single Isomorphous Replacement and Anomalous Scattering method and refined to 1.75Å resolution for both molybdate- and tungstate-bound crystal forms. The Rand free R factors are 16.2% and 20.3%, respectively, for the molybdate-bound model, and 16.3% and 18.6%, respectively, for the tungstate-bound model. Based on the structural comparisons with other periplasmic binding proteins, such as sulfate and phosphate binding proteins and ModA from Azotobactor vinelandii, the structural bases of the high specificity of ModA for molybdate were identified.

P. furiosus formaldehyde ferredoxin oxidoreductase (FOR) was crystallized m space group P2₁2₁2₁, with cell dimensions a=99.03Å, b=171.10Å, c=179.86Å, and α=β=γ=90°. Its crystal structure was solved by the molecular replacement method, and refined to 1.85Å resolution to an R factor of 17.4%, and free R factor of 22.0%. Complexes of FOR with glutarate, an inhibitor, and P. furiosus ferredoxin, its physiological electron acceptor, were solved and refined to 2.4Å and 2.15Å resolution, respectively. A structural comparison revealed that FOR may have an enzymatic mechanism similar to that of Desulfovibrio gigas Mop, an unrelated molybdenum-containing enzyme. Residues related to the substrate specificity of FOR were identified based on the FOR-glutarate interactions. From the arrangement of the redox centers in the FOR-ferredoxin complex, an electron transfer pathway between these two partners was proposed.

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