The angiopoietin-like protein ANGPTL4 catalyzes unfolding of the hydrolase domain in lipoprotein lipase and the endothelial membrane protein GPIHBP1 counteracts this unfolding

Abstract

Lipoprotein lipase (LPL) undergoes spontaneous inactivation via global unfolding and this unfolding is prevented by GPIHBP1 (Mysling et al., 2016). We now show: (1) that ANGPTL4 inactivates LPL by catalyzing the unfolding of its hydrolase domain; (2) that binding to GPIHBP1 renders LPL largely refractory to this inhibition; and (3) that both the LU domain and the intrinsically disordered acidic domain of GPIHBP1 are required for this protective effect. Genetic studies have found that a common polymorphic variant in ANGPTL4 results in lower plasma triglyceride levels. We now report: (1) that this ANGPTL4 variant is less efficient in catalyzing the unfolding of LPL; and (2) that its Glu-to-Lys substitution destabilizes its N-terminal α-helix. Our work elucidates the molecular basis for regulation of LPL activity by ANGPTL4, highlights the physiological relevance of the inherent instability of LPL, and sheds light on the molecular defects in a clinically relevant variant of ANGPTL4.DOI: http://dx.doi.org/10.7554/eLife.20958.001

Mapping the sites of the lipoprotein lipase (LPL)–angiopoietin-like protein 4 (ANGPTL4) interaction provides mechanistic insight into LPL inhibition

“…Therefore, many in vitro LPL activity assays and purification protocols use a bile acid, deoxycholate, to stabilize LPL (40, 50, 54 -58). In the presence of deoxycholate, nANGPTL4 inhibits LPL by a reversible, noncompetitive mechanism (40,54). Because LPL is known to have enhanced thermal stability within the biological fluids that contain bile acids, like serum and milk, we used them to better mimic physiological conditions in our kinetic assays (58,59).…”

Impaired thermogenesis and sharp increases in plasma triglyceride levels in GPIHBP1-deficient mice during cold exposure

“…Second, GPIHBP1 expression is crucial for the margination of triglyceride-rich lipoproteins (TRLs) along capillaries (4), allowing LPL-mediated triglyceride hydrolysis to proceed. Finally, in vitro biochemical studies have demonstrated that the binding of LPL to GPIHBP1 stabilizes LPL's hydrolase domain and preserves catalytic activity-even in the presence of ANGPTL4, an LPL inhibitor protein (5,6). …”

On the mechanism of angiopoietin-like protein 8 for control of lipoprotein lipase activity

“…ANGPTL4 consists of an N-terminal coiled-coil domain (ccd) and a C-terminal, fibrinogen-like domain. The N-terminal ccd of ANGPTL4 inactivates LPL by promoting dissociation of the active LPL dimer into inactive monomers (9,10). In this way, ANGPTL4 acts as a potent energy homeostasis switch causing reduced uptake of FAs from TG-rich lipoproteins in WAT during fasting (11,12).…”

“…It was previously demonstrated that the N-terminal ccd of ANGPTL3 reduces the activity of LPL in oxidative tissues in the fed state, thus directing the flow of lipoprotein-derived FAs to WAT for storage (14). In molar terms, ANGPTL3 is a relatively weak regulator of LPL in comparison to ANGPTL4 (10,15,16). Recent studies have shown, however, that the effect of ANGPTL3 on LPL is greatly enhanced by ANGPTL8 (15,17,18).…”