Structure of a key blood pressure regulator
About 1 in 3 American adults has high blood pressure. This increases their risk of many conditions, including heart attack, heart failure, and stroke.
One of the ways the human body regulates blood pressure is through a molecule called the angiotensin II type 1 receptor (AT1R). When the hormone angiotensin II binds to this receptor, it activates a pathway involving signaling molecules called G-proteins that constricts blood vessels and raises blood pressure. AT1R also activates other signaling pathways with different functions. For example, it can activate a pathway involving beta-arrestin proteins that reduces blood pressure and has other cardiovascular benefits.
High blood pressure is often treated with drugs called angiotensin receptor blockers (ARBs), which include losartan, candesartan, valsartan, irbesartan, telmisartan, and eprosartan. These drugs reduce blood pressure by blocking the G-protein pathway, relaxing and widening blood vessels. But they can also block the beneficial effects of AT1R and cause negative side effects, such as dizziness and headache. Designing drugs that block only the harmful G-protein pathway would allow the beneficial pathways to continue working as blood pressure is reduced. Creating such drugs would require detailed knowledge of AT1R's molecular structure, which has been difficult to figure out.
A team of researchers led by Dr. Vadim Cherezov at the University of Southern California used a novel X-ray crystallography technique called serial femtosecond crystallography to reveal the receptor's structure. Extremely bright, brief pulses of an X-ray free-electron laser allowed the researchers to obtain structural information from tiny micron-sized crystals at room temperature and without radiation damage. The study, which was partially funded by NIH's National Institute of General Medical Sciences (NIGMS) and National Heart, Lung, and Blood Institute (NHLBI), was published online in Cell on April 23.
The researchers were able to determine the structure of AT1R when bound to an angiotensin receptor blocker called ZD7155. They specifically identified the components that make up the receptor's binding pocket, where the blockers bind to cause their effects. Mutating these parts of the protein revealed which specific amino acids in the receptor were critical for binding. The researchers used this information to develop simulations of what happens in the binding pocket when other angiotensin receptor blockers bind to it.
Of current drugs, Cherezov says, "It's like using a 2-by-4 to kill a fly. Yes, it works, but perhaps a more refined approach could achieve the positive results without many side effects by only blocking the G-protein pathway while keeping the arrestin pathway active. To do so, you need to understand exactly how and where drug-like molecules bind to the receptor and what conformational changes they produce."
The researchers expect that their findings could lead to more effective drugs that cause fewer side effects.
-by Brandon Levy
--From the National Institute of Health
For further information on this and other health topics, visit the web site of the National Institute of Health at www.nih.gov.