Molecule of the Month: Angiotensin and Blood Pressure

Healthy blood pressure requires a delicate balance: the pressure needs to be high enough to circulate blood throughout the body, but not so high that it causes damage. Our bodies constantly monitor blood pressure and make changes if it gets out of the optimal range. The hormone angiotensin plays a central role in this control. It is released when blood pressure needs to be increased. It circulates through the body and has many effects, including constriction of blood vessels and making us feel thirsty.

Angiotensin performs its job in several steps. It is made by liver cells as a large inactive precursor called angiotensinogen, which is released into the bloodstream when needed. The small protease renin is released concurrently from the kidneys and it trims angiotensinogen to a small decapeptide, called angiotensin I. Angiotensin I is then clipped by ACE (angiotensin-converting enzyme), removing two more amino acids to form the octapeptide angiotensin II. Angiotensin II is the active hormone, binding to receptors on cell surfaces throughout the body and launching many processes that control flow of water and salt, releasing additional hormones, and contracting blood vessels.

We can explore the molecular details of all of these molecules in the PDB archive. As seen in the interactive JSmol below, we can compare structures of the inactive precursor of renin (PDB ID 3vcm) with the active form as it is clipping angiotensinogen (PDB ID 2x0b). ACE is a membrane-bound enzyme with two similar protein-cutting domains that cleave angiotensin I as well as other peptide hormones. The full structure is shown here from a computed structure model (AF_AFP12821F1), and many experimental structures of the individual domains are available in the archive. Structures are also available for angiotensin I (PDB ID 1n9u) and the receptor bound to angiotensin II (PDB ID 6os0).

By understanding the structures of proteins involved in the angiotensin signaling pathway, researchers have developed drugs to modify their action and lower blood pressure, if needed. The widely-used drug lisinopril is shown here, bound in the active site of the angiotensin-cutting domain of ACE (PDB ID 1o86). Because blood pressure management is so important for health, other drugs have been developed to block the action of all the other steps of the signaling pathway. For example, the interactive JSMol below includes a drug that blocks the action of renin.