Folding and Dynamics are Strongly pH-Dependent in a Psychrophile Frataxin

GONZÁLEZ-LEBRERO, RODOLFO MARTÍN; DEFELIPE, LUCAS A; MODENUTTI, CARLOS PABLO; ROITBERG, ADRIAN E.; BATASTINI, NICOLAS A.; NOGUERA, MARTIN E.; SANTOS, JAVIER; ROMAN, ERNESTO A.

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Lugar: Washington; Año: 2019

1520-6106

Protein dynamics, folding, and thermodynamics represent a central aspect of biophysical chemistry. pH, temperature, and denaturant perturbations inform our understanding of diverse contributors to stability and rates. In this work, we performed a thermodynamic analysis using a combined experimental and computational approach to gain insights into the role of electrostatics in the folding reaction of a psychrophile frataxin variant from Psychromonas ingrahamii. These folding reaction is strongly modulated by pH with a single, narrow and well-defined transition state with ~80% compactness, ~70% electrostatic interactions and ~60% hydration shell compared to the native state (αD=0.82, αH=0.67 and αΔCp=0.59). Our results are best explained by a two-proton/two-state model with very different pKa values of the native and denatured states (~5.5 and ~8.0, respectively). As a consequence, the stability strongly increases from pH 8.0 to 6.0 ( |ΔΔGo| = 5.2 kcal mol-1), mainly, because of a decrease in the TΔSo. Variation of ΔHo and ΔSo at pH below 7.0 is dominated by a change in ΔH?f and ΔS?f while at pH above 7.0 is governed by ΔH?u and ΔS?u. Molecular dynamics simulations showed that these pH modulation could be explained by the fluctuations of two regions, rich in electrostatic contacts, whose dynamics are pH-dependent and motions are strongly correlated. Results presented herein contribute to the understanding of the stability and dynamics of this frataxin variant, pointing to an intrinsic feature of the family topology to support different folding mechanism.