The structure of helical lipoprotein lipase reveals an unexpected twist in lipase storage

Abstract

Lipases are enzymes necessary for the proper distribution and utilization of lipids in the human body. Lipoprotein lipase (LPL) is active in capillaries, where it plays a crucial role in preventing dyslipidemia by hydrolyzing triglycerides from packaged lipoproteins. Thirty years ago, the existence of a condensed and inactive LPL oligomer was proposed. Although recent work has shed light on the structure of the LPL monomer, the inactive oligomer remained opaque. Here we present a cryo-EM reconstruction of a helical LPL oligomer at 3.8-Å resolution. Helix formation is concentration-dependent, and helices are composed of inactive dihedral LPL dimers. Heparin binding stabilizes LPL helices, and the presence of substrate triggers helix disassembly. Superresolution fluorescent microscopy of endogenous LPL revealed that LPL adopts a filament-like distribution in vesicles. Mutation of one of the helical LPL interaction interfaces causes loss of the filament-like distribution. Taken together, this suggests that LPL is condensed into its inactive helical form for storage in intracellular vesicles.

GPIHBP1 and ANGPTL4 Utilize Protein Disorder to Orchestrate Order in Plasma Triglyceride Metabolism and Regulate Compartmentalization of LPL Activity

“…Of note, LPL homodimers and monomers interconvert in vitro as judged by the rapid exchange of LPL protomers under conditions that favor interactions between LPL molecules (Lookene et al, 2004). As shown by cryo-electron microscopy (Gunn et al, 2020), LPL adopts a oligomeric conformation containing helical fibrils composed of head-to-tail LPL homodimers at high protein concentration and low temperature in the presence of high salt and heparin (Figure 2D). Once again, it seems likely that this oligomeric conformation is driven by the need to shield functionally important hydrophobic regions within LPL-the lid and substrate binding pocket in the hydrolase domain and the Trp-rich lipid-binding motif in the C-terminal PLAT domainfrom solvent exposure.…”

“…One of the two reciprocal dimer interfaces is shown in a close-up with the Trp-rich loop of one protomer occluding the active site of the other protomer. (D) In the presence of a high salt concentration or heparin, LPL may enter a higher oligomer state and form helical fibers (Gunn et al, 2020). The building blocks of these elongated fibers are the head-to-tail homodimers shown in (C).…”

“…Another possibility is that the Trp-rich loop of the PLAT domain is required for the assembly of head-to-tail LPL homodimers that are the minimal building blocks in the helical assembly of LPL oligomers. It is possible that these helical LPL oligomers associate with SDC-1 in secretory vesicles (Gunn et al, 2020). Further studies are required to define the conformation of LPL within the secretory pathway.…”

Comparison of angiopoietin-like protein 3 and 4 reveals structural and mechanistic similarities

“…The enzyme-coupled reaction is based on a colorimetric nonesterified fatty acid (NEFA) assay that we have previously used (58). The combination of NEFA assay and amplex was initially reported by Nimonkar et al (27), and we adapted their method to collect initial rate inhibition curves.…”

Current Diagnosis and Management of Primary Chylomicronemia

“…FFAs are used as an Lipoprotein lipase (LPL) hydrolyzes triglycerides (TGs) in TG-rich lipoproteins (TGRLs), such as very low-density lipoproteins (VLDLs) and chylomicrons (CMs) to liberate free fatty acids (FFAs), which are utilized by peripheral tissues (e.g., muscle, heart, and adipose tissues). Activity of LPL is regulated by a quaternary structure (monomer/dimer/oligomer) as well as by multiple LPL-pathway proteins [210][211][212] . LMF1 is required for the synthesis of LPL in parenchymal cells of these peripheral tissues.…”