Structural Insight into the Allosteric Coupling of Cu1 Site and Trinuclear Cu Cluster in CotA Laccase

In laccase, type 1 copper (Cu1) was connected to the trinuclear copper center (TNC) by the conserved Cys-His bridge. An allosteric coupling between the two redox sites has been reported; however, the molecular mechanism underlining the allosteric coupling is unknown. In this study, ligands of the two type 3 copper sites, including His491 and His493, in CotA were mutated to Cys or Ala. The crystal structures revealed that mutations at His491 and His493 caused rearrangement of the hydrogen-bond network and geometric distortion of the TNC, which severely impaired the activities of mutants H493A, H493C, and H491C. In addition, the change in TNC affected hydrogen bonds around Cys492 in the mutants and led to Cu1 being partially reduced. These results not only decipher the mechanism of allosteric coupling between Cu1 and TNC in laccase, but also pave the way for laccase protein engineering.