The type 1 copper site of pseudoazurin: Axial and rhombic

We report on a high-frequency electron-paramagnetic-resonance study of the type 1 copper site of pseudoazurin. The spectra fully resolve the contribution of a nearly axial spectrum besides the rhombic spectrum, which unequivocally proves the existence of two conformations of the copper site. Pseudoazurins have been considered from Achromobacter cycloclastes including eight mutants and from Alcaligenes faecalis. The two conformations are virtually the same for all pseudoazurins, but the rhombic/axial population varies largely, between 91/9 and 33/67. These observations are discussed in relation to optical absorption spectra and X-ray diffraction structures. A similar observation for fern plastocyanin from Dryopteris crassirhizoma suggests that dual conformations of type 1 copper sites are more common.

Graphical abstractEPR spectrum of pseudoazurin from Achromobacter cycloclastes, mutant Met16Trp, recorded at a microwave frequency of 275 GHz with contribution in red (axial component) and yellow (rhombic component).Figure optionsDownload full-size imageDownload as PowerPoint slide