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:
Rio de Janeiro
Reunión:
Encuentro; 18th ISMAR Meeting, 14th NMR Users Meeting, Vth Iberoamerican NMR Meeting Biomedical Imaging Symposium; 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 proteinprotein interactions and
membrane potential may optimize and regulate electronproton energy
transduction.