The dynamic properties of the M121H azurin metal site as studied by NMR of the paramagnetic Cu(II) and Co(II) metalloderivatives

The M121H azurin mutant in solution presents various species in equilibrium that can be detected and studied by 1H NMR of the Cu(II) and Co(II) paramagnetic metalloderivatives. In both cases up to three species are observed in slow exchange, the proportions of which are different for the two metalloderivatives. Above pH 5 the major species displays a tetrahedral coordination in which the His121 can be observed as a coordinated residue. Its metal site corresponds to a new type of site that is defined as a type 1.5 site. The second and third species resemble the wild type (type 1) azurin and, above pH 4.5, they are present only at a low concentration. At low pH a protonation process increases…