Control of KvLQT1 gating by KCNE proteins

Abstract

The structural changes underlying voltage-dependent gating in potassium channels are a subject of intense investigation, but relatively little is known about them. Mammalian channels are often complexed with accessory proteins that regulate or determine channel activity. KvLQT1 is a voltage-gated potassium channel that can associate with different accessory subunits of the KCNE gene family. The K+ current phenotype of KvLQT1 channels is completely different depending on which subunit it associates with. By domain swapping of KCNE1 and KCNE3 we determined that a group of three amino acids within the KCNE transmembrane domain were able to confer specificity in control of KvLQT1 activation kinetics, almost entirely due to a single amino acid within this triplet (T58 of KCNE1 and V72 of KCNE3). Control of KvLQT1 deactivation kinetics was not conferred by this region, however. To determine the region of KvLQT1 that interacts with these KCNE residues, we constructed a series of chimeras of KvLQT1 with potassium channels that either do not interact with KCNE-encoded proteins or interact but are not regulated by the association. We found that while a small region of the channel near the pore is sufficient to allow the KCNEs to bind to the KvLQT1, a more extended region of the channel is necessary to recapitulate the wild-type functional effects of the KCNE proteins. Within this region cysteine scanning uncovered a small stretch encompassing residues 338--340, that when mutated mirrored mutations at the previously identified critical KCNE residues. This region is believed to undergo a significant conformational change during the gating process, controlling access of potassium ions to the pore. Our work localizes KCNE proteins within the KvLQT1 channel to high resolution. By determining sites of binding and regulatory interaction we provide a model of K+ channel subunit association that will eventually be tested and solved by structural studies.