Unfolding of monomeric lipoprotein lipase by ANGPTL4: Insight into the regulation of plasma triglyceride metabolism

Kristian K. Kristensen, Katrine Zinck Leth-Espensen, Haydyn D.T. Mertens, Gabriel Birrane, Muthuraman Meiyappan, Gunilla Olivecrona, Thomas J.D. Jørgensen, Stephen G. Young, Michael Ploug*

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Abstrakt

The binding of lipoprotein lipase (LPL) to GPIHBP1 focuses the intravascular hydrolysis of triglyceride-rich lipoproteins on the surface of capillary endothelial cells. This process provides essential lipid nutrients for vital tissues (e.g., heart, skeletal muscle, and adipose tissue). Deficiencies in either LPL or GPIHBP1 impair triglyceride hydrolysis, resulting in severe hypertriglyceridemia. The activity of LPL in tissues is regulated by angiopoietin-like proteins 3, 4, and 8 (ANGPTL). Dogma has held that these ANGPTLs inactivate LPL by converting LPL homodimers into monomers, rendering them highly susceptible to spontaneous unfolding and loss of enzymatic activity. Here, we show that binding of an LPL-specific monoclonal antibody (5D2) to the tryptophan-rich lipid-binding loop in the carboxyl terminus of LPL prevents homodimer formation and forces LPL into a monomeric state. Of note, 5D2-bound LPL monomers are as stable as LPL homodimers (i.e., they are not more prone to unfolding), but they remain highly susceptible to ANGPTL4-catalyzed unfolding and inactivation. Binding of GPIHBP1 to LPL alone or to 5D2-bound LPL counteracts ANGPTL4-mediated unfolding of LPL. In conclusion, ANGPTL4-mediated inactivation of LPL, accomplished by catalyzing the unfolding of LPL, does not require the conversion of LPL homodimers into monomers. Thus, our findings necessitate changes to long-standing dogma on mechanisms for LPL inactivation by ANGPTL proteins. At the same time, our findings align well with insights into LPL function from the recent crystal structure of the LPL GPIHBP1 complex.

OriginalsprogEngelsk
TidsskriftProceedings of the National Academy of Sciences of the United States of America
Vol/bind117
Udgave nummer8
Sider (fra-til)4337-4346
ISSN0027-8424
DOI
StatusUdgivet - 25. feb. 2020

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