Effect of tyrosine nitration on electron shuttle and peroxidase activity of cytochrome c

MARIA ANA CASTRO; DAMIÁN ALVAREZ PAGGI; VERÓNICA TÓRTORA; RAFAEL RADI; MARCELO A. MARTI; DARÍO A. ESTRÍN; DANIEL H. MURGIDA

Salta

Congreso; 3rd Latin American Protein Society Meeting; 2010

Cytochrome c is a small globular protein with a hexacoordinated heme. It is not only involved in the mitochondrial electron transfer but may also participate as an apoptosis trigger and as an activator of peroxidase activity after post-translational modifications take place, such as tyrosine nitration, or upon interaction with the membrane lipid cardiolipin. It has been observed that nitration of Tyr-74 results in an early alkaline transition1 with the consequent displacement of the axial Met-80 ligand. This effect is proposed to be the result of a steric destabilization of the flexible -loop and not a consequence of the deprotonation of the tyrosine. The role of Tyr-67 in transmitting this perturbation in a solvent-accessible residue to the heme site has been analysed using both molecular dynamic simulations and hybrid QM/MM calculations. The important interaction between Met-80 and Tyr-67 is also monitored by comparing the electrochemical behaviour of the WT protein vs. the Y67F mutant. Thermodynamic (E0) and kinetic (kET, reorganization energy) parameters for several mutants were obtained in order to further characterize the effect of the nitration on the redox properties, which may themselves play a major role in a gain-of-function scheme for Cyt when apoptosis is triggered.