The human potassium channel KCNQ1 is a polytopic, helical membrane protein responsible for repolarization of heart muscle cells after the action potential, as well as water and salt homeostasis in several epithelial tissues. Malfunctioning KCNQ1 leads to various diseases, the most common of which are associated with heart disease. In the heart, KCNQ1 associates with the accessory protein KCNE1 to form the potassium channel largely responsible for the duration of the action potential. KCNQ1 and/or KCNE1 loss-of-function mutations have severe phenotypes resulting in loss of hearing and long QT syndrome. Gain-of-function mutations have been linked to sudden infant death syndrome (SIDS), familial atrial fibrillation and short QT syndrome. One such mutation that has been characterized in vivo, V141M in KCNQ1, is completely dependent on KCNQ1 association with KCNE1 and is thought to be a part of a cleft in the three-dimensional structure, where several gain-of-function mutations are located. Several disease-inducing polymorphisms within KCNQ1 and KCNE1 are single amino acid mutations within the transmembrane region. Although several homology models of KCNQ1 exist, these models are not interpretable to high resolution; this low degree of confidence is due to the low sequence identity between the four helical bundle transmembrane domain that confers voltage sensitivity to KCNQ1 (voltage-sensor domain; Q1-VSD) and previously determined, homologous structures (~20%). Utilizing the V141M and the known lock-on Q1-VSD (E160R-Q234E) mutations, the goal of this project is to build a reliable, experimentally-restrained, atomic-resolution structure of the open state of Q1-VSD:KCNE1 complex, which will be used to explain the etiology of the family of atrial fibrillation- inducing mutations, including V141M. The proposed research consists of three parts: 1) determine the structure of the open state Q1-VSD, 2) generate in vitro restraints between KCNE1 and Q1-VSD with and without the V141M mutation, and 3) generate structure-function restraints using electrophysiology, ultimately applying all of the restraints in the modeling software Rosetta to dock the voltage sensor domain to KCNE1. Developing an experimentally-constrained atomic-resolution model of the transmembrane domain of KCNQ1 as it complexes with KCNE1 promises to elucidate the structural underpinnings of the many disease-inducing mutations associated with this complex.