Structural Proteomics Sheds New Light on Mechanisms Improving Cardiovascular Health

The Science                                  

Our heart health relies on removing extra cholesterol that builds up in arteries due to high levels of low-density lipoproteins, often referred to as “bad cholesterol.” High-density lipoproteins (HDL), or “good cholesterol,” extract this excess cholesterol from arteries, transporting it to the liver for elimination. HDLs are a group of small complexes of proteins and fats, each with a unique structure and role. One key protein, apolipoprotein (APO)A2, found on most HDLs, had an unclear function that Pacific Northwest National Laboratory (PNNL) researchers wanted to understand. Within the Predictive Phenomics Initiative, an internal investment that supports discovery of the biological function of complex systems, researchers used advanced technologies to uncover that APOA2 interacts with other key proteins on HDL particles, enhancing their ability to remove cholesterol from arteries.

The Impact

Coronary heart disease is the leading cause of death in the United States and thus there remains a major need for strategies that improve cardiovascular health. This work not only provided a long-sought understanding of the function of APOA2 on HDL particles, but also revealed that HDLs containing APOA2 are viable therapeutic targets that can protect against the development of coronary heart disease. 

Summary

HDLs are structurally and functionally diverse nano-sized particles that circulate in the blood and carry out a variety of essential biological functions. Over the last decade, it has become clearer that the protein and lipid composition of a particular HDL particle elegantly regulates its function. For decades, the function of APOA2 on HDL eluded investigators despite being the second most abundant protein on HDL. In this study, researchers used an advanced structural proteomics technology called limited proteolysis-based mass spectrometry (LiP-MS) to probe how APOA2 impacts the structure and function of HDL. Unlike conventional proteomics techniques, LiP-MS pin-points structurally altered regions within a protein complex. This provides researchers with a clear picture of how APOA2 reconfigures a key region of a partner protein, APOA1, which increases the particle's ability to dock onto cells on the arterial wall and effectively extract the excess cholesterol. Findings were validated using strategic mutations that removed the key region on APOA1, which resulted in the particle having a diminished ability to accept cholesterol. This study underscores the effectiveness of high-throughput structural proteomics tools in providing novel biological insights into protein interactions and function. 

Research Contacts

John T. Melchior, john.melchior@pnnl.gov, PNNL

Snigdha Sarkar, snigdha.sarkar@pnnl.gov, PNNL

Funding

The research described in this paper is part of the Predictive Phenomics Initiative at PNNL and conducted under the Laboratory Directed Research and Development program. PNNL is a multiprogram national laboratory operated by Battelle for the Department of Energy under Contract No. DE-AC05-76RL01830.