Amyloid-like aggregation of a human apolipoprotein A-I variant

RAMELLA, N.; TRICERRI, M. A.; SANCHEZ, S. A.; FERREIRA, S. T.; RIMOLDI. O. J.

Baltimore, USA

Congreso; Biophysical Society 53rd Annual Meeting; 2009

Biophysical Society

Amyloidosis are characterized by extra cellular deposits of anomalous fibrilar proteins. Human apolipoprotein A-I (apoA-I) is not normally involved within these pathologies. However, one case of severe amyloidosis associated with atherosclerosis was observed when apoA-I shows a deletion of a lysine residue in a central region of the protein (apoA-I Lys107-0). In order to get insight on the local cellular environment that promotes this anomalous aggregation, we studied the folding of the deletion mutant, as compared with wild type apoA-I (Wt). Analysis of chemical denaturation and by using hydrostatic pressure show that apoA-I Lys107-0 is more unstable and has a stronger tendency to form b sheet structure as incubation time increases, specially at acidic pH. Under these conditions, mutant denaturation is less cooperative, suggesting intermediate states folding. In order to confirm that these states prone protein aggregation, we followed protein folding by two-Photon Fluorescence Correlation Spectroscopy. Our results clearly show that, even at very low concentrations, protein aggregation is detected, under acidic conditions, after incubation for a few hours at 37oC. Interestingly, also Wt suffers conformational chances that favor some insoluble states. These results suggest that the anomalous aggregation of apoA-I Lys 107-0, is mediated by intermediate folded states and b sheet conformation, induced by an acidic pH. Protein misfolding is concentration-dependent, but can occur under diluted solutions. We discuss our results in terms of the pathological landscape of atherosclerosis.