Correlated electric field modulation of electron transfer parameters and the access to alternative conformations of multifunctional cytochrome c

SPEDALIERI, CECILIA; TÓRTORA, VERÓNICA; OVIEDO-ROUCO, SANTIAGO; TOMASINA, FLORENCIA; MURGIDA, DANIEL H.; SCOCOZZA, MAGALÍ F.; RADI, RAFAEL

BIOELECTROCHEMISTRY

ELSEVIER SCIENCE SA

Año: 2022 vol. 143

1567-5394

Cytochromec(Cytc) is a multifunctional protein that, in its native conformation, shuttles electrons in themitochondrial respiratory chain. Conformational transitions that involve replacement of the heme distalligand lead to the gain of alternative peroxidase activity, which is crucial for membrane permeabilizationduring apoptosis. Using a time-resolved SERR spectroelectrochemical approach, we found that the keyphysicochemical parameters that characterize the electron transfer (ET) canonic function and those thatdetermine the transition to alternative conformations are strongly correlated and are modulated by localelectric fields (LEF) of biologically meaningful magnitude. The electron shuttling function is optimized atmoderate LEFs of around 1 V nm1. A decrease of the LEF is detrimental for ET as it rises the reorganiza-tion energy. Moreover, LEF values below and above the optimal for ET favor alternative conformationswith peroxidase activity and downshifted reduction potentials. The underlying proposed mechanism isthe LEF modulation of the flexibility of crucial protein segments, which produces a differential effecton the kinetic ET and conformational parameters of Cytc. These findings might be related to variationsin the mitochondrial membrane potential during apoptosis, as the basis for the switch between canonicand alternative functions of Cytc. Moreover, they highlight the possible role of variable LEFs in determin-ing the function of other moonlighting proteins through modulation of the protein dynamics.