Understanding the role of apolipoprotein A-I in atherosclerosis. Post-translational modifications synergize dysfunction?

Abstract

BackgroundThe identification of dysfunctional human apolipoprotein A-I (apoA-I) in atherosclerotic plaques suggests that protein structure and function may be hampered under a chronic pro inflammatory scenario. Moreover, the fact that natural mutants of this protein elicit severe cardiovascular diseases (CVD) strongly indicates that the native folding could shift due to the mutation, yielding a structure more prone to misfold or misfunction. To understand the events that determine the failure of apoA-I structural flexibility to fulfill its protective role, we took advantage of the study of a natural variant with a deletion of the residue lysine 107 (K107del) associated with atherosclerosis. MethodsBiophysical approaches, such as electrophoresis, fluorescence and spectroscopy were used to characterize proteins structure and function, either in the native conformation or under oxidation or intramolecular crosslinking. ResultsK107del structure was more flexible than the protein with the native sequence (Wt) but interactions with artificial membranes were preserved. Instead, structural restrictions by intramolecular crosslinking impaired the Wt and K107del lipid solubilization function. In addition, controlled oxidation decreased the yield of the native dimer conformation for both variants. ConclusionsWe conclude that even though mutations may alter protein structure and spatial arrangement, the highly flexible conformation compensates the mild shift from the native folding. Instead, post translational apoA-I modifications (probably chronic and progressive) are required to raise a protein conformation with significant loss of function and increased aggregation tendency. General SignificanceThe results learnt from this variant strength a close association between amyloidosis and atherosclerosis. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=95 SRC="FIGDIR/small/142844v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@265244org.highwire.dtl.DTLVardef@1e30814org.highwire.dtl.DTLVardef@279375org.highwire.dtl.DTLVardef@421fd9_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights-Oxidation is clue to induce protein misfolding -Natural mutation does not seem critical as a sole reason to determine pathogenicity -Atherosclerosis and amyloidosis are closely related -Intramolecular crosslinking restrains protein flexibility and function