Thermodynamics and kinetics of the folding of a psychrophilic frataxin variant

GONZÁLEZ LEBRERO RODOLFO M.; NOGUERA MARTIN E.; RIGAL JUAN B.; DEFELIPE LUCAS; GONZÁLEZ FLECHA LUIS; ALMEIDA FABIO; SANTOS JAVIER; ROMAN ERNESTO A.

Salto

Congreso; Latin American Crosstalk in Biophysics and Physiology; 2015

Frataxin participates in iron-sulfur cluster assembly and is involved inFriedreich´ Ataxia, a neurodegenerative disease. We studied the stabilizationand dynamics of a variant from the psychrophilic bacteria (pFXN). pFXN stability is highly modulated by pH (1). Here we studied the effect of pH on pFXN folding. A two-state model with two-protonation sites analysis showed that transition and native states are highly perturbed by pH with apparent pKa values for native and unfolded states of 8.4 and 7.5, and 4.5 and 7.1, respectively, revealing a strong shift in the pKa upon folding. Perturbation with pH and temperature showed that stabilization comes mainly from the entropic contribution to the folding free Gibbs energy. This might be a result of a difference in the solvation due to protonation states in native and unfolded ensembles. This effect was explored in the presence of co-solvents. Molecular dynamics showed that glutamic residues shift pKa to 6-7.5. Our results show that both stability and dynamics of pFXN are strongly modulated by pH. The abnormal ∆Cp of pFXN upon folding might be related to the psychrophilic nature of the organism in which pFXN has evolved, suggesting implications on its function.(1) Ernesto A. Roman et al. Frataxin from Psychromonas ingrahamii as a Model to Study Stability Modulation within the CyaY Protein Family. Biochim. Biophys. Acta (2013).This worked was supported with ANPCyT, UBA and CONICET grants