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Effect of histidine 6 protonation on the active site structure and electron-transfer capabilities of pseudoazurin from Achromobacter cycloclastes

Lookup NU author(s): Dr Katsuko Sato, Professor Christopher Dennison

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Abstract

The paramagnetic 1H NMR spectrum of Cu(II) pseudoazurin [PACu(II)] contains eight, directly observed hyperfine-shifted resonances which we have assigned using saturation transter experiments on a 1:1 mixture of PACu(I) and PACu(II). The spectrum exhibits a number of similarities to those of other cupredoxins, but differences are found concerning the Cu-S(Met)interaction. The spectrum is dependent on pH* in the range 8.5-4.5 (pKa* 6.4), and a conformational change involving movement of the copper ion away from the Met toward the equatorial ligands, as a consequence of protonation of the surface His6 residue, is identified. Corresponding changes are also seen in the UV/vis spectrum. The protonation/deprotonation equilibrium of His6 influences the reduction potential of the protein in the same pH range. The self-exchange rate constant of PACu at pH* 6.0 (25°C) is considerably smaller (1.1 × 103 M-1 s-1) than the value obtained at pH* 7.6 (3.7 × 103 M-1 s-1). The effect on the self-exchange reactivity is mainly due to an alteration in the reorganization energy of the copper site brought about by the structural change resulting from His6 protonation.


Publication metadata

Author(s): Sato K; Dennison C

Publication type: Article

Publication status: Published

Journal: Biochemistry

Year: 2002

Volume: 41

Issue: 1

Pages: 120-130

ISSN (print): 0006-2960

ISSN (electronic): 1520-4995

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/bi0117448

DOI: 10.1021/bi0117448

PubMed id: 11772009


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