Chemical Exchange at the Trinuclear Copper Center of Small Laccase from Streptomyces coelicolor

Abstract

The trinuclear copper center (TNC) of laccase reduces oxygen to water with very little overpotential. The arrangement of the coppers and ligands in the TNC is known to be from many crystal structures, yet information about possible dynamics of the ligands is absent. Here, we report dynamics at the TNC of small laccase from Streptomyces coelicolor using paramagnetic NMR and electron paramagnetic resonance spectroscopy. Fermi contact-shifted resonances tentatively assigned to histidine Hδ1 display a two-state chemical exchange with exchange rates in the order of 100 s^-1. In the electron paramagnetic resonance spectra, at least two forms are observed with different g_z-values. It is proposed that the exchange processes reflect the rotational motion of histidine imidazole rings that coordinate the coppers in the TNC.