IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Alternative ground states in copper proteins unveiled by NMR spectroscopy: A novel view for biological electron transfer
Autor/es:
A. J. VILA; ABRIATA LA; MORGADA, MARCOS; M.E. ZABALLA
Lugar:
San Pablo
Reunión:
Workshop; The Magnetic Resonance in Biology workshop in São Paulo; 2013
Resumen:
NMR of oxidized copper proteins has been largely overlooked, mostly due to the slow electron relaxation times of Cu2+ ion which induce extremely fast relaxation rates in nearby nuclei, rendering them undetectable. It has been shown, however, that these unfavorable electron relaxation features are restricted to T2 copper sites, since T1, T3 and CuA centers display faster electron relaxation rates which make them amenable to NMR studies. In all these cases, the fast electron relaxation stems from to the availability of low-lying excited electronic states which is due to the particular electronic structure of these centers. These features are strongly related to the physiological requirements of these copper centers to perform efficient electron transfer or oxidation chemistry. The binuclear copper sites CuA and T3 display particularly fast electron relaxation rates which are due to low-lying excited states that can be populated at room temperature and contribute to the reactivity of the metal site. Other magnetic techniques, such as EPR, ENDOR and MCD, normally recorded at cryogenic temperatures, are able to monitor exclusively the ground state. NMR in solution, instead can shed light on the availability of these invisible electronic states. We have carried on detailed studies in the CuA site, involved in long range electron transfer in terminal oxidases. NMR discloses the fact that the CuA site can exist in two alternate ground states with different orbital symmetry, which are invisible to other techniques.  We show that thermal fluctuations may populate two alternative ground-state electronic wave functions optimized for electron entry and exit, respectively, through two different and nearly perpendicular pathways. These findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover, it is shown that this energy gap and, therefore, the equilibrium between ground states can be fine-tuned by minor perturbations, suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction.