A comparative analysis of the folding and misfolding pathways of the third PDZ domain of PSD95 investigated under different pH conditions

作者：Murciano Calles Javier; Cobos Eva S; Mateo Pedro L; Camara Artigas Ana; Martinez Jose C^*

来源：Biophysical Chemistry, 2011, 158(2-3): 104-110.

DOI：10.1016/j.bpc.2011.05.018

• Folding intermediates
• Protein thermodynamics and stability
• Pdz domains
• Oligomerization processes
• Annular/spherical aggregates
• Amyloid fibrils

Equilibrium unfolding at neutral pH of the third PDZ domain of PSD95 is well described by the presence of a partly unfolded intermediate that presents association phenomena. After some days' incubation annular and fibrillar structures form from the oligomers. At pH values below 3, however, differential scanning calorimetry shows that PDZ3 seems to unfold under a two-state scheme. Kinetic measurements followed by dynamic light scattering, ThT and ANS fluorescence reveal that the misfolding pathway still exists despite the absence of any populated intermediates and shows an irreversible assembling of the supramacromolecular structures as well as an appreciable lag-phase, contrary to what is found in similar experiments at neutral pH. Moreover, as shown by transmission-electron-microscopy images, the annular structures seen at neutral pH completely disappear from incubated solutions. According to the structural information, this titration behavior appears to be the consequence of a conformational equilibrium that depends on the protonation of some Glu residues located at the C-terminal alpha 3 helix and at the hairpin formed by strands beta 2 and beta 3. Our calculations suggest that the enthalpic contribution of these interactions may well be as much as 40 kJ.mol(-1). The possible regulatory role of this equilibrium upon PDZ3 functionality and amyloid formation is briefly discussed.

• 出版日期2011-10