Abstract 412: In Silico Structural and Metabolic Profiling of Non-Synonymous Single Nucleotide Polymorphisms in APOA-I Gene

Abstract

Mature apoA-I contains 243 residues organized in two-domains as N-terminal four-helix bundle and C-terminal two helices. Cholesterol interaction with both lipid-free and lipid-bound apoA-I may be one of the key events in amyloidosis and reverse cholesterol transport (RCT). By the SIFT score, 20 non-synonymous missense mutations in APOA-I gene, located almost exclusively in N-domain, may impair apoA-I function. A majority (4 from 5) of putative cholesterol recognition amino acid consensus (CRAC: L/V-X(1-5)-Y-X(1-5)-R/K) and a single cholesterol consensus motif (CCM: R/K-X(2-6)-I/L/V-X(3)-W/Y) aligned within/between helices in the bundle. Importantly, CRAC2 in apoA-I co-aligned with CRAC2 in apoE and CRAC4 in apoA-IV. A short four amino acid sequence L44-L47 may present disorder-to-order transitioning binding region in apoA-I as predicted by molecular recognition feature (MoRF). Indeed, CCM corresponded to unstructured region with low stability in lipid-free apoA-I. Stabilizing effect due to the direct cholesterol-peptide interaction with the involvement of CRAC1 (L14-K23) and/or CCM (K40-W50) in amyloidogenic peptide 1-93 is suggested to underlie the known effect of cholesterol on the induction of helix formation in this peptide. Cholesterol may be speculated to act in helix formation as a chemical chaperone thus triggering disorder-to-order transition within MoRF; without cholesterol, this MoRF may be involved into protein-protein interaction. Indeed, the association of W50R substitution with the accelerated mutant aggregation rate and the involvement of L44-S55 segment into cross-beta-sheet formation were demonstrated by others. Also, D102H substitution in CRAC2 (V97-K106) may be harmful in RCT. With PDBe Motifs and Sites algorithm, cholesterol is a ligand for L101, F104 and W108 residues in CRAC2 motif of apoA-I in nascent HDL. Besides, the resistance of two-domain apoA-I structure to denaturation by GuHCl is sensitive to cholesterol level in discoidal HDL. Overall, different CRACs may contribute into amyloidosis-connected apoA-I misfolding and cholesterol efflux for lipid-free apoA-I. Cholesterol binding to lipid-bound apolipoprotein may change the structural plasticity of two domains and/or their relative dimensions.