Lipoprotein lipase requires a flexible lid and stable C-terminal, both maintained by ApoC-II peptide binding.

Lipoprotein lipase (LPL) is the rate-limiting enzyme responsible for hydrolyzing triglycerides in circulating lipoproteins. Reduced LPL activity contributes to hypertriglyceridemia, a major cardiovascular risk factor. LPL activity is thought to depend on the conformation of the lid domain, the lipid pore, N- and C-terminal domains (NTD, CTD), and stabilization of these domains by endogenous activators such as apolipoprotein C-II (ApoC-II). Despite major clinical significance, the structure-function relationship of LPL's functional domains and cofactors remain incompletely understood. To address this, we performed the longest known (1-μs) molecular dynamics simulations of LPL independently and in complex with an ApoC-II mimetic peptide (ApoC-II-P). For the first time, we show that LPL's flexible lid can adopt multiple orientations, transitioning between open and closed states that regulate lipid pore access and catalytic activity. We also observed 'flipping' of ~180° by the CTD, a unique characteristic that dictates LPL activity when not in a closed lid state. Furthermore, ApoC-II-P stabilizes LPL by bridging its NTD and CTD, while maintaining an optimal lid orientation. Biochemical and cellular assays corroborate these findings, demonstrating that ApoC-II-P enhances LPL hydrolysis and supports noncanonical LPL functions. Together, these insights reveal previously unrecognized mechanisms governing LPL regulation and activity dynamics.