Frataxin from Psychromonas ingrahamii as a model to study stability modulation in the CyaY protein family

ERNESTO A. ROMAN; SANTIAGO E. FARAJ; ALEXANDRA COUSIDO-SIAH; ANDRÉ MITSCHLER; ALBERTO PODJARNY; JAVIER SANTOS

San Javier, Tucumán

Congreso; XLI Reunión Anual de la Sociedad Argentina de Biofísica; 2012

Sociedad Argentina de Biofísica

Friedrich´s Ataxia is an autosomal disorder caused by the lack of functional frataxin protein. In our group we are studying the relation between stability,functionality, and flexibility within CyaY protein family. Here we focused on frataxin from Psychromonas ingrahamii (pFXN), an extreme psychrophile sea-ice bacterium which can grow at -12 °C. Structural and stability characterization of pFXN was performed by X-ray crystallography, far- and near-UV CD, tryptophan fluorescence, and molecular dynamic simulations. The solved structure at 1.45Å of apo-pFXN show that this protein shares the general structural features of the CyaY protein family. Although our results show that the native conformation of pFXN is not altered in the range of pH between 6-8, unfolding experiments reveals that it is more stabilized at pH 6. Crystal soaking with Europium and Cobalt revealed binding sites. B-factor analysis of the obtained structures show that the region spanning residues 20-30, residues 60-70, and the C-terminus are the most mobile within the crystallographic packing in the apo form, decreasing their value in the holo form. Computational experiments show that protonation of H67 or H44 decrease the RMSF of these most mobile regions, in addition to the decrease in their own environment. We suggest that the electrostatic network that include these histidine residues might alter not only the local mobility, but also global dynamics and stability. This would be one of the mechanisms in the CyaY family to control protein stability and function.