Crystal structure of Pseudomonas aeruginosa apo‐azurin at 1.85 Å resolution

Abstract

The 3D structure of apo-azurin from Pseudomonas aeruginosa has been determined at 1.85 Å resolution. The crystal structure is composed of two different molecular forms of apo-azurin arranged as hetero-dimers in the tetramer of the asymmetric unit. Form 1 closely resembles the holo-protein lacking copper. Form 2 shows differences in the metal binding site region induced by the incorporation of a solvent molecule into this site. The positions of the copper ligands His⁴⁶ and His¹¹⁷ are shifted by 0.6 Å and 1.6 Å. The His¹¹⁷ side chain adopts a position at the surface of the protein, thereby facilitating access to the copper site. The presence of two different molecular forms of apo-azurin in the crystal lattice may reflect an equilibrium between the two forms in solution. ¹H-NMR spectra or apo-azurin recorded as a function or pH show that at high pH the line broadening of His³⁵, His⁴⁶ and His¹¹⁷ resonances is consistent with an interconversion between forms 1 and 2. At low pH, no broadening is observed. This may indicate that here the interconversion is fast on the NMR timescale.