UV resonance Raman and NMR spectroscopic studies on the pH dependent metal ion release from pseudoazurin

Stabilization of protein structure through π-π interaction in the second coordination sphere of pseudoazurin

Noncovalent, weak interactions in the second coordination sphere of the copper active site of Pseudoazurin (PAz) from Achromobacter cycloclastes were examined using a series of Met16X variants. In this study, the differences in protein stability due to the changes in the nature of the 16th amino acid (Met, Phe, Val, Ile) were investigated by electrospray ionization mass spectrometry (ESI-MS) and far-UV circular dichroism (CD) as a result of acid denaturation. The percentage of native states (folded holo forms) of Met16Phe variants was estimated to be 75% at pH 2.9 although the wild-type (WT), Met16Val and Met16Ile PAz, became completely unfolded. The high stability under acidic conditions is correlated with the result of the active site being stabilized by the aromatic substitution of the Met16 residue. The π-π interaction in the second coordination sphere makes a significant contribution to the stability of active site and the protein matrix.

Paramagnetic1H NMR Spectrum of the Cobalt(II) Derivative of Spinach Plastocyanin

The native type 1 copper ion of spinach plastocyanin has been substituted with Co(II). The UV/vis spectrum of this derivative is similar to those for other Co(II)-substituted cupredoxins. The paramagnetic 1H NMR spectrum of Co(II) plastocyanin has been completely assigned. A number of similar studies on Co(II) cupredoxins have been published, but this is the first such analysis of a substituted plastocyanin that possesses the archetypal type 1 active site. A truly representative comparison of the available paramagnetic 1H NMR data for Co(II) cupredoxins is now possible. We demonstrate in this work that there is very little difference in the metal-ligand contacts between the Co(II) derivatives of cupredoxins possessing a type 1 axial site (plastocyanin) and those having perturbed (rhombic) spectroscopic features.