Analysis of the crystal structure of MtPMO3* deposited by Span et al. indicate that the second shell His161 corresponding to NcLPMO9D His157 is present in two conformations: an "inward" copperfacing conformation with a with a Cu-Ne distance of ~5 Å, and an "outward" copper-distant conformation with a Cu-Ne distance of ~10 Å (Fig. ). The experimentally observed existence of both "inward" and "outward" conformations indicates mobility of the conserved second shell histidine, at least when the copper active site is solvent exposed.