The Acidic Domain of the Endothelial Membrane Protein GPIHBP1
RESEARCH ARTICLE The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain Simon Mysling1,2,3, Kristian Kølby Kristensen1,2, Mikael Larsson4, Anne P Beigneux4, Henrik Ga˚ rdsvoll1,2, Loren G Fong4, Andre´ Bensadouen5, Thomas JD Jørgensen3, Stephen G Young4,6, Michael Ploug1,2* 1Finsen Laboratory, Rigshospitalet, Copenhagen, Denmark; 2Biotech Research and Innovation Centre, University of Copenhagen, Copenhagen, Denmark; 3Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark; 4Department of Medicine, University of California, Los Angeles, Los Angeles, United States; 5Division of Nutritional Science, Cornell University, Ithaca, United States; 6Department of Human Genetics, University of California, Los Angeles, Los Angeles, United States Abstract GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL.GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1.LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/ mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in *For correspondence: m-ploug@ regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity finsenlab.dk by mitigating the global unfolding of LPL’s catalytic domain.
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