Abstract
Heritable mutations in renal potassium channel ROMK cause a severe salt and water balance disorder called antenatal Bartter syndrome (ABS). Of more than 30 ABS mutations identified, about half are located in the intracellular domain of the channel; the mechanisms underlying channel dysfunction for most of these mutations are unknown. By mapping intracellular mutations onto an atomic model of ROMK, we found that several are localized to an ancient immunoglobulin (Ig)‐like domain (IgLD) that has not been characterized previously, prompting us to examine it in detail. The IgLD is assembled from two β‐pleated sheets packed face to face, creating a β‐sheet interface, or core, populated by highly conserved side chains. Thermodynamic calculations on computationally mutated channels indicate that IgLD core residues are among the most important residues for determining cytoplasmic domain stability. We show that two ABS mutations located within the IgLD core impair channel trafficking in mammalian cells. A fraction of core mutant channels reach the cell surface, but they are electrically silent due to closure of the helix‐bundle gate. Compensatory mutation‐induced rescue of channel function revealed that IgLD core mutants fail to rectify. Our study sheds new light on the pathogenesis of ABS and provides a novel framework for understanding Kir channel cytoplasmic domain structure‐function relations.
Published Version
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