Frataxin from Psychromonas ingrahamii as a model to study stability modulation within CyaY family

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

San Javier, Tucumán, Argentina

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 functionalfrataxin protein. In our group we are studying the relation between stability,functionality, and flexibility within CyaY protein family. Here we focusedon frataxin from Psychromonas ingrahamii (pFXN), an extremepsychrophile sea-ice bacterium which can grow at -12 °C. Structural andstability characterization of pFXN was performed by X-ray crystallography,far- and near-UV CD, tryptophan fluorescence, and molecular dynamicsimulations. The solved structure at 1.45Å of apo-pFXN show that thisprotein shares the general structural features of the CyaY protein family.Although our results show that the native conformation of pFXN is notaltered in the range of pH between 6-8, unfolding experiments reveals that itis more stabilized at pH 6. Crystal soaking with Europium and Cobaltrevealed binding sites. B-factor analysis of the obtained structures show thatthe region spanning residues 20-30, residues 60-70, and the C-terminus arethe most mobile within the crystallographic packing in the apo form,decreasing their value in the holo form. Computational experiments showthat protonation of H67 or H44 decrease the RMSF of these most mobileregions, in addition to the decrease in their own environment. We suggestthat the electrostatic network that include these histidine residues might alter not only the local mobility, but also global dynamics and stability. Thiswould be one of the mechanisms in the CyaY family to control proteinstability and function.