(197am) Determination of the Lipidated Structure of ApoE through Various in silico Methods

Apolipoprotein E (ApoE), a major scaffold protein in lipoproteins, plays an important role in transporting lipids to microglial surface proteins to regulate brain lipid metabolism. ApoE has three isoforms (ApoE2/3/4), with ApoE4 considered to be the greatest known genetic risk factor for late onset Alzheimer’s disease (AD). Despite much experimental evidence illustrating the impact of ApoE isoform on AD pathology, little in silico work has been established. This is largely due to the lack of available lipidated ApoE structures, as the only published crystal structure is of unlipidated ApoE3. Herein, we describe the use of two different computational approaches to obtain structures of the different ApoE isoforms in their lipidated forms, which we then rigorously compared to recently published experimental data. Specifically, we employed: (1) steered molecular dynamics (MD) simulations to bias the hinge regions of ApoE towards a conformation resembling ApoE in its lipidated form, and (2) homology modeling of ApoE against a published crystal structure of ApoA1 in a dimerized, lipid-bound, horseshoe-like conformation. A lipid nanodisc was then added to the structures using CHARMM-GUI, and MD simulations were performed to investigate the feasibility and stability of the structures in solvent. Overall, this work serves to elucidate the molecular-level changes that occur to ApoE as it becomes lipidated, paving the way for future in silico studies into the interactions of lipidated ApoE and many different proteins with prominent roles in neurodegenerative disease settings.