Influencia del pH en la estabilidad termodinámica de una variante psicrófila de frataxina.

ERNESTO A ROMÁN; INES BURGOS; JAVIER SANTOS

Buenos Aires

Congreso; Sociedad Argentina de Biofísica; 2011

Sociedad Argentina de Biofísica, Fundación Leloir

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> Friedrich's Ataxia is an autosomal disorder caused by the lack of functional frataxin protein. In our group we are focusing on the relation between stability, function, and dynamics involved in frataxin's fold operativity. Here we present the role of sequence determinants on the pH stabilization of the native structure of a psicrophile variant of frataxin. Our results show that pFXN reversibly unfolds in a cooperative fashion in the presence of urea and GndHCl, at lower concentrations than the ones needed to unfold human frataxin. Also, as for the hFXN, ionic strenght extremely increases its stability. However, pFXN varies its stability upon incubation at different pHs in the range of 6.0-8.0. This seems to be the only up to date frataxin variant with this behaviour. Melting temperature goes from 37C at pH 8.0 to 67C at pH 6.0. Differential scanning calorimetry shows that this unfolding occurs with an intermediate whose stability is also modulated by pH, and is less populated at pH 6.0. Bioinformatic analysis revealed the presence of a two stacked histidines in the beta sheet that could be responsible for the stabilization process. Also, computer simulations showed that protonation of these histidines favor the interaction between them and the rest of the protein, while favor the repulsion between both residues. This result agrees with the decrease of native Trp fluoresnce at pH 6.0 where interaction between Trp and this histidine is favored. Alltogether, we found a putative role of sequence determinants in stability modulation by pH. This could be important in physiological situations where stability needs to be smoothly modulated. Moreover, the existance of this motif could be a tool to modify stability of native proteins in different enviromental conditions.