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The Active-Site Structure of Umecyanin, the Stellacyanin from Horseradish Roots

Lookup NU author(s): Professor Christopher Dennison, Dr Dr MD Harrison Harrison


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The type 1 copper sites of cupredoxins typically have a His2Cys equatorial ligand set with a weakly interacting axial Met, giving a distorted tetrahedral geometry. Natural variations to this coordination environment are known, and we have utilized paramagnetic 1H NMR spectroscopy to study the active-site structure of umecyanin (UMC), a stellacyanin with an axial Gln ligand. The assigned spectra of the Cu(II) UMC and its Ni(II) derivative [Ni(II) UMC] demonstrate that this protein has the typical His 2Cys equatorial coordination observed in other structurally characterized cupredoxins. The NMR spectrum of the Cu(II) protein does not exhibit any paramagnetically shifted resonances from the axial ligand, showing that this residue does not contribute to the singly occupied molecular orbital (SOMO) in Cu(II) UMC. The assigned paramagnetic 1H NMR spectrum of Ni(II) UMC demonstrates that the axial Gln ligand coordinates in a monodentate fashion via its side-chain amide oxygen atom. The alkaline transition, a feature common to stellacyanins, influences all of the ligating residues but does not alter the coordination mode of the axial Gln ligand in UMC. The structural features which result in Cu(II) UMC possessing a classic type 1 site as compared to the perturbed type 1 center observed for other stellacyanins do not have a significant influence on the paramagnetic 1H NMR spectra of the Cu(II) or Ni(II) proteins.

Publication metadata

Author(s): Dennison C, Harrison MD

Publication type: Article

Publication status: Published

Journal: Journal of the American Chemical Society

Year: 2004

Volume: 126

Issue: 8

Pages: 2481-2489

ISSN (print): 0002-7863

ISSN (electronic): 1943-2984

Publisher: American Chemical Society


DOI: 10.1021/ja0375378

PubMed id: 14982457


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