Tuning redox properties in novel type 1 copper sites by controlling second sphere structural features.

SZUSTER, JONATHAN; ZITARE, ULISES A.; LEGUTO, ALCIDES J.; REBECHI, JUAN P.; ALEJANDRO J. VILA; DANIEL H. MURGIDA

Florianópolis

Congreso; 18th International Conference on Biological Inorganic Chemistry (18ICBIC); 2017

Society of Biological Inorganic Chemistry(SBIC)

In this work we report the functional characterization of a series of novel type 1 copper sites (T1) that were produced by introducing different loop sequences from a selected group of native T1 into the protein matrix of the soluble domain of the subunit II of the ba3 oxidase from Thermus thermophilus (Tt-CuA), which is a cupredoxin as well. These new chimeric variants show notable differences in their UV-visible spectra when compared to those from their native scaffold as well as significant upshifts of redox potential of about 100mV, implying a highly perturbed metal site geometry. Notably, these changes were achieved without altering the first coordination ligand set. The entropy and enthalpy contributions to E° were obtain by cyclic voltammetry experiments. These contributions show a partially compensation behaviour, a phenomena which was previously related to reaction-induced changes in solvent organization and interactions within the protein hydration sphere. We propose that some structural features of the loops, like length and the identity of residues involved in the hydrogen bonding network, might be responsible for these thermodynamic trend by controlling the solvent-metal site interplay. In addition, reorganization energies were obtained from the Arrhenius plot of the heterogeneous electron transfer constant (kET) determined by protein-film voltammetry experiments using Laviron´s method. Two groups, with high and low reorganization energy values, were defined. All chimeric variants within each group share common characteristics among their loop sequence.Altogether these results suggest the possibility of tuning the reduction thermodynamics (∆Hº y ∆Sº), and the reorganization energy, by modifying the hydrogen bonding pattern and loop length at the second sphere level. It also provides a platform from which one can raise even more the E° by site directed mutagenesis of the first and second sphere residues as it was already shown in previous work.