ARRA: Delayed Rectifier K Channel Biogenesis is Unveiled in Models of Long QT Syndrome

The principal subunits for voltage-gated K+ channels (Ky) are the pore-forming a-subunits. Mutations in the Ky a-subunit 11.1 (Kvl 1.1) are linked to type 2 Long QT syndrome LQT2. Most LQT2-linked missense mutations disrupt the biogenesis of Kvl 1.1. The proposed sequence of events during Ky biogenesis in the Endoplasmic Reticulum (ER) are: 1) membrane insertion and asparagine-linked (N-linked) `core' glycosylation, 2) oligomerization of a- and auxiliary subunits, 3) formation of the pore and voltage sensor, and 4) formation of proximity between adjacent amino (NH2) and carboxy (COOH) termini. Complexes of molecular chaperone and co-chaperone proteins called "chaperomes" interact with Ky proteins during biogenesis to create an environment, the `folding solvent,' which facilitates proper protein folding. There are dozens of different members of chaperones and co-chaperones that can comprise a chaperome. These complexes recognize misfolded proteins and target these proteins for degradation via the ubiquitin and proteosome pathway. Therefore, chaperomes regulate the ER Associated Folding (ERAF) and ER Associated Degradation (ERAD) pathways. The purpose of this administrative supplement is to initiate several experiment outlined in the parent application that explore the mechanism(s) that underlie the ER retention & the LQT2-linked mutations, N470D- and R751W-Kvl 1.1. These mutations were selected because they each exhibit distinct trafficking phenotypes (patterns) when incubated in 27oC or E-4031 for 24hrs, suggesting they may interrupt the trafficking of Kvl 1.1 at discrete steps in Kvl 1.1 biogenesis. This supplement tests the hypothesis that these LQT2 mutations are retained in the ER by different mechanisms. Specifically we predict that the ERAF/ERAD of these mutations is differentially regulated by the lecithin chaperone calnexin, and that these mutations will have different mobility coefficients in the ER. We anticipate that these experiments will provide mechanistic insight as to whey LQT2 mutations exhibit different patterns of correction, and perhaps identify novel therapeutic strategies that can increase the ER export of LQT2 mutations.