CONICET | Buscador de Institutos y Recursos Humanos

The native folding of proteins is critical to fulfill their biological functions. Some proteins are structurally unstable and thus, small changes in the medium are clue to induce a pathological conformation. Amyloidosis is characterized by extra cellular deposits of anomalous fibrilar proteins. Human apolipoproteinA-I (apoA-I ) is not usually associated with this pathology, but some natural single mutants induce severe amyloidosis in patients. In order to get insight on the local cellular environment that promotes this anomalous aggregation, we studied the influence of low pH (a microenvironment associated to inflammation) that, in vivo, could induce protein misfolding and toxicity. We expressed and purified two natural- occurring apoA-I mutants: Gly26Arg (a substitution mutant with a gain in a positive charge), and Lys107-0 (showing a deletion of a Lisine residue). Structural analysis shows that acidic pH induces a strong conformational shift, decreasing the cooperative denaturation pattern, and the hydrophobic cavities present in the native state of the protein. This means that misfolding could be associated with intermediate folding states, and protonation of residues. Even though natural pathological mutants show higher tendency to aggregate as amyloid-like structures, wt apoA-I also is sensitive to acid-induced misfolding. Proteins show a significant structural arrangement between pH 5 and 6, suggesting strong influence of protein charge in such events. In addition, low pH enhances the binding of apoA-I and the mutants to heparin, a component of the cellular matrix that could help to retain the protein in injured environments being substrate for oxidative aggression. We conclude that local pH is clue to ensure the native conformation of apoA-I, and natural mutants are more sensitive to mild modifications, eliciting protein pathological rearrangement