Edward Yu, professor of pharmacology at the School of Medicine, led a team of researchers in publication of an article titled “Inhibition mechanism of NKCC1 involves the carboxyl terminus and long-range conformational coupling, leading to arrest of the cotransporter” in Science Advances.
The team included the following Case Western Reserve University researchers in the Department of Pharmacology:
- Mitchell Moseng, postdoctoral fellow;
- Chih-Chia Su, assistant professor;
- Meinan Lyu, instructor; and
- Philip A Klenotic, research assistant.
About the research
The ability for cells to uptake ions such as sodium, potassium and chloride is of utmost importance as these ions are critical for the cells to maintain their normal function. In humans, the membrane-bound Na-K-2Cl cotransporter-1 (NKCC1) is broadly expressed in the brain, lung, intestine and exocrine systems to facilitate the uptake of these ions. There is strong evidence that disruption of NKCC1 leads to intestinal and pulmonary obstruction, pancreatic insufficiency, chronic gastrointestinal diseases, lung infections, acute and chronic pain, sensorineural hearing loss, and possibly neurodevelopmental disorders. Loop diuretics such as bumetanide and furosemide act in the kidney loop of Henle to inhibit NKCC2, a related transporter that reclaims part of the sodium that is filtered in the urine. The loop diuretic is used to increase water excretion and treat disorders like congestive heart failure and other disorders involving water retention. Interestingly, the loop diuretics are also effective inhibitors of NKCC1, and possibly effective drugs for neurological disorders. In particular, bumetanide has been shown to attenuate the severity of several neurodevelopmental disorders, including autism spectrum disorders and Fragile X syndrome. How these drugs interact with NKCC1 has not been fully determined.
In this study, researchers used cryo-electron microscopy to solve the structures of NKCC1 in the absence and presence of the two drugs.
These structures showed that there are two distinct drug binding sites on the transporter and that drug binding results in significant changes in the overall structure of the cotransporter, closing the narrow pathway that allows the ions to be transported across. Indeed, in a process known as long-distance conformational coupling, these drugs not only cause structural changes locally where they bind, but also affect the overall topology of the cotransporter. These structural changes, in turn, inhibit the ability of NKCC1 to transport ions. By fully understanding the mechanism that these compounds use to inhibit NKCC1, additional drugs affecting NKCC1 can be designed, drugs that for instance might differentiate NKCC1 and NKCC2, or drug that might better cross the blood-brain barrier and therefore more effectively affect the transporter where it matters the most for the neurodevelopmental disorders.