INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Protonation modulates stability by regulating mobility of psychrophilic frataxin variant C-terminal region
FABIO ALMEIDA; ADRIAN ROITBERG; LUCAS A. DEFELIPE; ANWAR IQBAL; JAVIER SANTOS; CARLOS MODENUTTI; RODOLFO GONZALEZ-LEBRERO; ERNESTO ROMAN
Congreso; ISCB Latin America; 2016
Asociación argentina de bioinformática y biología computacional
It has been previously seen in equilibrium unfolding experiments that frataxin from Psychromonas ingrahamii (pFXN) stability is increased as pH lowers with an apparent pKa around 7.4. However, exploration of kinetic mechanism revealed that folding proceeds with an apparent pKa around 5.5 while unfolding around 8.5. The fact that histidine point mutants did not suppress stability pH modulation suggests that other residues have their pKa shifted with respect to their reference values. In the present work, we study the pKa of residues in the folded state of pFXN and a model mesophilic FXN (Escherichia coli FXN, eFXN) which has been reported not to change its stability in the range that pFXN does, by means of Replica Exchange Constant pH Molecular Dynamics (RECpHMD) simulations. RECpHMD simulations showed that there are glutamic acid residues located in the main loop that have their pKa shifted towards pH 6-7. Preliminary NMR titration experiments showed that apparent pKa of residues located in the main loop region are shifted. Exploration of crystallographic structures and RECpHMD revealed a complex hydrogen bonded interaction network highly modulated by protonation. Furthermore, a strong increase in mobility of the C-Terminal loop is observed in pFXN between pH 6 and 8 only present in this variant. The fact that the length of C-terminal of FXN variants is correlated with their stability has been previously reported by our and other groups.This work gives aid in understanding stability modulation of frataxin and propose a strategy to intervene this modulation.