Download Protein misfolding associated to mild modifications of local cellular pH

Protein misfolding associated to mild modifications of local cellular pH:
Amyloid-like aggregation of human apolipoprotein A-I variants
Ramella N., Tricerri M. A., Rimoldi O.J.
INIBIOLP-CONICET. Fac. Ciencias Medicas, UNLP. Argentina
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 Lys1070 (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.
Keywords: apolipoprotein A-I, protein misfolding, amyloidosis.
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