Structural basis for distinct functions of the naturally occurring Cys mutants of human apolipoprotein A-I[S]

• Main Authors: Olga Gursky, Martin K. Jones, Xiaohu Mei, Jere P. Segrest, David Atkinson
• Format: Article
• Language: English
• Published: Elsevier 2013-12-01
• Series: Journal of Lipid Research
• Subjects: Milano and Paris mutations; double-belt and trefoil/tetrafoil conformations; protein-lipid interactions; protein dynamics and function; atherosclerosis
• Online Access: http://www.sciencedirect.com/science/article/pii/S0022227520356789

HDL removes cell cholesterol and protects against atherosclerosis. ApoA-I provides a flexible structural scaffold and an important functional ligand on the HDL surface. We propose structural models for apoA-IMilano (R173C) and apoA-IParis (R151C) mutants that show high cardioprotection despite low HDL levels. Previous studies established that two apoA-I molecules encircle HDL in an antiparallel, helical double-belt conformation. Recently, we solved the atomic structure of lipid-free Δ(185–243)apoA-I and proposed a conformational ensemble for apoA-IWT on HDL. Here we modify this ensemble to understand how intermolecular disulfides involving C173 or C151 influence protein conformation. The double-belt conformations are modified by belt rotation, main-chain unhinging around Gly, and Pro-induced helical bending, and they are verified by comparison with previous experimental studies and by molecular dynamics simulations of apoA-IMilano homodimer. In our models, the molecular termini repack on various-sized HDL, while packing around helix-5 in apoA-IWT, helix-6 in apoA-IParis, or helix-7 in apoA-IMilano homodimer is largely conserved. We propose how the disulfide-induced constraints alter the protein conformation and facilitate dissociation of the C-terminal segment from HDL to recruit additional lipid. Our models unify previous studies of apoA-IMilano and demonstrate how the mutational effects propagate to the molecular termini, altering their conformations, dynamics, and function.