New Partners For Cholesterol

Cholesterol is a molecule of many talents: It regulates membrane structure and is a precursor for many signaling molecules. It is, of course, best known as an indicator of cardiovascular disease.

New findings suggest that cholesterol may have an even broader effect on human metabolism. The work shows that cholesterol interacts with virtually all major classes of proteins.

Benjamin F. Cravatt and coworkers at Scripps Research Institute developed three probes to construct a proteome-wide map of the proteins that interact with cholesterol (Nat. Methods, DOI: 10.1038/nmeth.2368). They used the probes to fish out more than 800 proteins, many of which weren’t known to interact with cholesterol.

Each probe consists of a modified cholesterol scaffold with added photoreactive and alkyne groups. When exposed to ultraviolet light, the probe’s photoreactive diazirine ring cross-links to proteins that would normally interact with cholesterol. Reporter tags for enrichment, which is needed for detection and identification by quantitative mass spectrometry, can be attached to the alkyne. The researchers characterized the interacting proteins by using quantitative mass spectrometry.

They found three major sugar-metabolizing enzymes that interact with cholesterol, suggesting that cholesterol may have a previously unknown role in helping regulate sugar metabolism. Cholesterol also interacts with several enzymes in the sterol biosynthetic pathway, indicating that it may also help regulate its own biosynthesis.

“Hopefully, this method can be extended to identify the molecular sites of cross-linking and thus cholesterol binding,” says Patrick van der Wel, an assistant professor of structural biology at the University of Pittsburgh School of Medicine. “It already presents an opportunity to identify sensible protein targets that may facilitate in-depth in vitro studies of the biophysical and structural underpinnings of cholesterol binding.”

“We are currently evaluating the sterol-interacting proteome in cell models of cancer and lipid-storage disorders,” Cravatt says. “I suspect that the resulting sterol-protein interaction profiles may illuminate dysregulated pathways and mechanisms that explain the biochemical basis for disease, as well as identify potential targets for therapeutic intervention.”