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. 2019 May 21;116(21):10360-10365.
doi: 10.1073/pnas.1820171116. Epub 2019 May 9.

Structure of lipoprotein lipase in complex with GPIHBP1

Rishi Arora  1 , Amitabh V Nimonkar  2 , Daniel Baird  1 , Chunhua Wang  1 , Chun-Hao Chiu  1 , Patricia A Horton  1 , Susan Hanrahan  2 , Rose Cubbon  2 , Stephen Weldon  3 , William R Tschantz  3 , Sascha Mueller  4 , Reto Brunner  5 , Philipp Lehr  4 , Peter Meier  4 , Johannes Ottl  5 , Andrei Voznesensky  3 , Pramod Pandey  1 , Thomas M Smith  1 , Aleksandar Stojanovic  4 , Alec Flyer  6 , Timothy E Benson  1 , Michael J Romanowski  7 , John W Trauger  8
Affiliations

Structure of lipoprotein lipase in complex with GPIHBP1

Rishi Arora et al. Proc Natl Acad Sci U S A. .

Abstract

Lipoprotein lipase (LPL) plays a central role in triglyceride (TG) metabolism. By catalyzing the hydrolysis of TGs present in TG-rich lipoproteins (TRLs), LPL facilitates TG utilization and regulates circulating TG and TRL concentrations. Until very recently, structural information for LPL was limited to homology models, presumably due to the propensity of LPL to unfold and aggregate. By coexpressing LPL with a soluble variant of its accessory protein glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) and with its chaperone protein lipase maturation factor 1 (LMF1), we obtained a stable and homogenous LPL/GPIHBP1 complex that was suitable for structure determination. We report here X-ray crystal structures of human LPL in complex with human GPIHBP1 at 2.5-3.0 Å resolution, including a structure with a novel inhibitor bound to LPL. Binding of the inhibitor resulted in ordering of the LPL lid and lipid-binding regions and thus enabled determination of the first crystal structure of LPL that includes these important regions of the protein. It was assumed for many years that LPL was only active as a homodimer. The structures and additional biochemical data reported here are consistent with a new report that LPL, in complex with GPIHBP1, can be active as a monomeric 1:1 complex. The crystal structures illuminate the structural basis for LPL-mediated TRL lipolysis as well as LPL stabilization and transport by GPIHBP1.

Keywords: GPIHBP1; LPL; X-ray crystallography; lipase.

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Conflict of interest statement

Conflict of interest statement: All authors are current or former employees of Novartis Institutes for Biomedical Research or Novartis Pharma AG, and some are also shareholders of Novartis. This work was funded by Novartis Institutes for Biomedical Research.

Figures

Fig. 1.
Fig. 1.
Crystal structures of LPL/sGPIHBP1 and LPL-2/sGPIHBP1. (A) Ligand-free LPL/sGPIHBP1 structure in space group C121 showing the head-to-tail arrangement of two LPL molecules in the asymmetric unit. The active site serine residue is represented with a space-filling model, and the bound Ca2+ ion is represented by a sphere. The N-terminal acidic domain of GPIHBP1 and portions of the lid and lipid-binding regions of LPL (indicated by dashed lines) are not visible in the crystal structure. (B) Structure of the LPL-2/sGPIHBP1 complex in space group P21212 in which two molecules of 2 are bound to the active site. Two of the four LPL/sGPIHBP1 complexes in the asymmetric unit are shown to illustrate the head-to-tail arrangement of LPL molecules. The LPL lid (highlighted in green) and lipid-binding region (highlighted in blue) are visible in the crystal structure. As in the ligand-free structure, the N-terminal acidic domain of GPIHBP1 is not visible.
Fig. 2.
Fig. 2.
(A) The lid region of LPL (highlighted in blue) in the LPL-2/sGPIHBP1 structure. The active site serine residue is shown as a space-filling model, and the lipid-binding region from the adjacent LPL molecule is highlighted in green. (B) Alignment of LPL with PL with a focus on the lid region. PL is shown in orange with its lid region highlighted in red.
Fig. 3.
Fig. 3.
The lipid-binding region (highlighted in green) of LPL in the LPL-2/sGPIHBP1 structure. The lid region of the adjacent LPL molecule is highlighted in blue.
Fig. 4.
Fig. 4.
Surface representations of LPL in the LPL-2/sGPIHBP1 structure (compound 2 is not shown). (A) LPL lipophilicity surface. Green, violet, and white shadings represent hydrophobic, hydrophilic, and neutral surfaces, respectively. (B) LPL electrostatic surface. Red, blue, and white shadings represent acidic (negative), basic (positive), and neutral surfaces, respectively.
Fig. 5.
Fig. 5.
(A) Detail of the head-to-tail interaction between adjacent LPL molecules in the ligand-free LPL/sGPIHBP1 structure in space group C121. (B) In the LPL-2/sGPIHBP1 structure, binding of 2 to the active site displaces Trp420 and Trp421 from the active site of the neighboring LPL molecule.
Fig. 6.
Fig. 6.
SEC analysis of the LPL/sGPIHBP1 complex. The elution peak for Avi-His6-FLAG-LPL/sGPIHBP1 (in black) is overlaid with the elution peaks for BioRad gel filtration standards (in blue). The results of MALS analysis of these elution peaks are shown in Table 1.
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