(389ah) Lipoprotein Lipase’s Stability Is Mediated By Apoc-II Binding at the Lid and C-Terminal Domains

Lipoprotein lipase (LPL) hydrolyzes triglycerides within lipoproteins to liberate fatty acids and facilitate uptake. The hydrolytic activity of LPL is dependent on the structural conformation of several functional domains within the protein, including the lipid pore, lid domain and lipid binding site. Furthermore, LPL activity relies on the binding of activating factors, such as Apolipoprotein C-II (ApoC-II), which in turn stabilize these structural domains. LPL activity is low in individuals with diabetes and contributes to hypertriglyceridemia¾a major risk factor for cardiovascular diseases. We have previously developed a peptide mimetic of ApoC-II that can potently increase LPL activity, potentially serving as a therapeutic for diabetic dyslipidemia. However, the molecular mechanisms underlying the LPL-ApoC-II peptide interaction remain elusive and must be resolved prior to drug development efforts.

We conducted the longest all-atom molecular dynamics simulations of LPL and the ApoC-II peptide known to date to establish biologically relevant structures that can be confidently used in simulations to investigate protein-peptide interactions. We simulated various conformations of the LPL-ApoC-II complex based on their experimentally determined binding sites. To further validate our computational findings, we performed circular dichroism and biochemical lipase assays to determine how the ApoC-II peptide maintains LPL structural integrity.

We discovered LPL’s flexible lid domain determines accessibility to the lipid hydrolysis site. We further observed that ApoC-II can stabilize LPL through two mechanisms, one by locking the lid domain into open or closed states, and the second by maintaining the C-terminal domain’s conformation. Moreover, when LPL was incubated at 20°C or 40°C for 30 minutes, LPL activity was reduced, indicating loss of structure. However, in the presence of ApoC-II, the time- and heat-associated loss of hydrolytic activity was markedly reduced. Overall, our findings show that LPL’s lid conformation is important for mediating variable ApoC-II binding, and thus LPL stability and hydrolytic activity.