Coordination effects on the electronic structure of the CuA site of cytochrome c oxidase

► The CuA site has an electronic structure appropriate for a rapid electron transfer. ► The ligand coordination effects of the CuA site of CcO were investigated. ► His ligation provides strong orbital and electrostatic effects. ► The coordination of the peptide group of Glu gives only electrostatic effects. ► The coordination of Met provides weak orbital and electrostatic effects.