Solved: BIDMC-led Scientists Solve Sixty Year Old Puzzle

Structure of enzyme that produces fuel for the heart of muscle cells revealed 

After sixty years of intensive investigation by biochemists and physiologists worldwide, a team of scientists led by Gabriel Birrane Ph.D, a structural biologist at Beth Israel Deaconess Medical Center (BIDMC), has provided the first detailed picture of the structure of the lipoprotein lipase (LPL) protein. The team’s findings, published in The Proceedings of the National Academy of Sciences, offer a better understanding of cardiovascular metabolism and could open the door to targeted treatment for several rare cardiovascular disorders. 

LPL breaks down triglycerides in the bloodstream to produce fuel for the heart and muscle cells and delivers nutrients to vital tissues. Deficiencies in LPL can elevate the risk for coronary artery disease, while increased LPL levels may lead to insulin resistance and obesity. LPL’s central role in cardiac metabolic processes makes it an attractive therapeutic target, but development of such therapies remained stymied as long as LPL’s chemical structure was unknown.  

Birrane and colleagues were able to achieve what generations of scientists before them were not thanks to recent discoveries by his collaborators, co-senior authors Muthuraman Meiyappan, PhD of Takeda Pharmaceuticals;  Stephen Young, MD, of the  David Geffen School of Medicine at  University of California, Los Angeles; and Michael Ploug, PhD, at the University of Copenhagen.

“Because LPL alone is not very stable, previous experimenters had difficulty producing sufficient amounts LPL for structural analysis,” explained Birrane, an Instructor of Medicine in the Division of Experimental Medicine in the Department of Medicine at BIDMC and Harvard Medical School “My collaborators provided the breakthrough data, including methods to purify active LPL and a companion protein that was crucial to stabilize LPL. With this knowledge, we concentrated our efforts on crystallizing a complex of the two proteins. Crystals of the complex produced x-ray data of much higher quality than we were able to obtain with LPL alone and this allowed us to analyze the structure at a molecular level.” 

In earlier work, Meiyappan and his team found that a protein called LMF1 is needed to allow cells to produce large quantities of LPL. Young’s groups discovered that another protein, called GPIHBP1, is required for the normal functioning of LPL, and Ploug showed that without GPIHBP1, LPL is rapidly degraded. “Together, these observations provided our team at BIDMC with the tools needed to produce large amounts of stable LPL protein for crystallization, data collection and structural analysis,” said Birrane. 

Now that the team has revealed the structure of the protein complex, researchers can understand how mutations in LPL or GPIHBP1 lead to elevated triglyceride levels and coronary artery disease. Other molecules bind to and regulate the function of LPL. In follow up studies, Birrane and his collaborators would like to determine these molecules’ mechanism of action, information that will allow scientists to better understand the role LPL plays in cardiovascular disease and diabetes.        

In addition to Birrane, Young, Ploug and Meiyappanc, investigators included Anne P. Beigneux and  Loren G. Fong of  the Department of Medicine, David Geffen School of Medicine, University of California; Brian Dwyer, Bettina Strack-Logue, Omar L. Francone and Clark Q. Pan of c Discovery Therapeutics, US Drug Discovery, Shire Pharmaceuticals; Kristian Kølby Kristensen of Finsen Laboratory, Rigshospitalet; and Haydyn D. T. Mertens of BIOSAXS Group, European Molecular Biology Laboratory. 

This research was supported by Fondation Leducq Transatlantic Network Grant 12CVD04; National Institutes of Health Grants HL090553, HL087228 , HL125335, and HL139725; Lundbeck Foundation Grant R230-2016-2930 ; and NOVO Nordisk Foundation Grants NNF17OC0026868 and NNF18OC0033864. Research was partly funded by Shire US Drug Discovery.

Disclosures: Dwyer, Strack-Logue, Pan and Meiyappanc are employees of Shire and hold stock and stock options in Shire. Young are coordinators on a Leducq Transatlantic Network Grant. They have not collaborated directly on this project.