The further, the closer: degenerate ground-states in CuA sites

LEGUTO, ALCIDES J.; LANCASTER, KYLE; MORGADA, MARCOS N.; SMITH, MA; VILA, ALEJANDRO J.

Florianopolis

Conferencia; 18th International Conference on Biological Inorganic Chemistry; 2017

CuA is a binuclear copper site present in highly efficient electron-transfer metalloproteins.1 In the oxidized state, CuA center is a mixed valence pair. Its electronic structure which can be described by two alternative ground-states: u* and πu. The πu ground-state is higher in energy, and is partially populated at room temperature, rapidly interconverting with u*.2, By replacing a native Met axial copper ligand, redox potential and u*/πu energy gap can be decreased in 400 cm-1 in a M160H mutant.3 Recently, the Tt3L chimeric protein was created replacing three loops surrounding CuA by their eukaryotic homologous, thus only incorporating second-sphere perturbations.4 This chimera also shows a decrease in the u*/πu energy-gap from 600 cm-1 in WT protein to 240 cm-1. Herein we report the characterization at room temperature and low temperature of a mutant in which we combine first- and second-sphere mutations (Tt3L-M160H). This mutant is characterized by two degenerate u*/πu levels at room temperature, showing that these mutations have additive effects on the electronic structure without any severe geometric perturbations. Moreover, when comparing with other CuA site containing variants, a clear trend within Cu-Cu distance and πu state population is shown. These results indicate that Cu-Cu distance may be important in regulating electronic properties of the site at room temperature, as longer Cu-Cu distances correspond to a decreased u*/πu energy gap. At low temperature, the trend is lost as πu state population decreases in all variants by thermal stabilization.Acknowledgments: CONICET, ANPCyTReferences 1. Solomon, E. et al. Chem. Rev. 114, 3659 (2014). 2. Abriata, L. et al. J. Am. Chem. Soc. 131, 1939 (2009). 3. Abriata, L. et al. Proc. Nat. Acad. Sci. 109, 17348 (2012). 4. Morgada, M. et al. Angew. Chem. Int. Ed. 53, 6188 (2014).