MIMICKING THE INITIAL STEPS OF AGGREGATION USING LOW CONCENTRATIONS OF TFE: THE CONFORMATIONAL COALESCENCE OF THE IFABP ABRIDGED FAMILY

CARLA R. ANGELANI; MICHELLE PONCINO; JULIO J. CARAMELO; JOSÉ M. DELFINO; LUCRECIA MA. CURTO

Sierra de la Ventana, Buenos Aires

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Biofísica (SAB).; 2014

Δ98Δ and Δ78Δ are two all-β sheet variants of IFABP (intestinal fatty acid binding protein). These frameworks became useful to study the molecular determinants related to aggregation of β-barrel proteins. Albeit displaying increased conformational plasticity, these variants exhibit a native-like topology and are able to support a cooperative folding behavior. At odds with the established notion that a perturbation of the native fold should necessarily favor the population of aggregation-prone species, we have demonstrated that the intrinsic stability of these proteins (ΔG°H2O:IFABP≥Δ78Δ>Δ98Δ) does not bear a straightforward correlation with their aggregation propensity triggered by trifluoroethanol (TFE: Δ78Δ>IFABP>Δ98Δ). In this scenario, it might be more insightful to correlate aggregation propensity with the stability measured in the presence of this co-solvent. With this in mind, we initially characterize the changes in conformation and stability of this protein family upon the addition of a sub-aggregating concentration of TFE (10% v/v). This treatment brings about the coalescence of all three proteins into conformations richer in β content and more akin in stability, as shown by thermal ramps and exposure to chemical denaturants. New biophysical measurements include high resolution NMR, binding of ANS and quenching of intrinsic fluorescence. The cumulative evidence supports the hypothesis that the conformational changes observed would represent those leading to the aggregation-prone species.