Folding of a natural variant of human apolipoprotein A-I associated with atherosclerosis. Micro environment and function

GISONNO, R.; DIAZ LUDOVICO, I; TRICERRI, M. A.; RAMELLA, N.; GARDA, H. A.; GONZALEZ, M. C.

San Luis

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Biofísica; 2019

Sociedad Argentina de Biofísica

Human apolipoprotein A-I, the major protein fraction of the High density lipoproteins (HDL) has long been considered a protective factor against the development of coronary heart disease. However, either the deletion of a residue (Lys 107) or a chronic pro-inflammatory scenario resulted in the deposition of the protein within atherosclerosis plaques and associated to amyloid deposits. The presence of protein aggregates in this landscape may suggest that a shift from the native conformation should result in a loss of function. To elucidate whether structural changes may be responsible for the protein deposition and misfunction, we compared by biophysical approaches the deletion mutant Lys107-0 structure with respect to the protein with the native sequence (Wt), either freshly resuspended or after controlled oxidation. A red shift in intrinsic Trp fluorescence and a higher binding of Bis ANS indicate a more flexible structure of this mutant, which preserves lipid binding capacity. Structural flexibility seems to be clue to this role, as a lower efficiency in intra-chain cross linking resulted in lower blockage of dimirystoyl phosphatidyl choline (DMPC) clearance. In order to analyze the effect of oxidation on protein structure and function, Wt and Lys107-0 were oxidized and protein structure reevaluated. Trp and Met oxidation is detected by Mass Spec, and an increased tendency of the proteins to aggregate is observed by microscopy approaches, which is especially evident for the deletion mutant. Nevertheless, lipid clearance and solubilization is not significantly modified, indicating that the integrity of the salt bridge network involving polar residues in the central domain of the protein is not essential to this function. More research will be done to determine the importance of single residues in protein function. AcknowledgementsAuthors acknowledge fundings of ANPCyT (PICT 2016-0849) and UNLP (M187)