Deletion of the HERG C-terminal 147 amino acids exposes an RGR endoplasmic reticulum retention signal that abolishes I_Kr current by preventing protein trafficking to the cell surface.
Does deletion or mutation of the C-terminal amino acids of HERG affect I_Kr current and protein trafficking?
The study identifies that a key function of the HERG C-terminal 104 amino acids is to mask an ER retention signal, explaining the molecular mechanism of defective trafficking in LQT2.
Mutations in the humanEther-à-go-go-Related gene (HERG), encoding the protein underlying the cardiac K+ current, IKr, cause chromosome 7-linked long QT syndrome (LQT2). In this study, we show that deletion of the C-terminal 147 amino acids (HERGΔ147) abolished IKr, whereas a larger, 159-amino acid deletion (HERGΔ159) identified in an LQT2 kindred did generate IKr, albeit with reduced amplitude compared with the wild type. The 12 amino acids present in HERGΔ147 and absent in HERGΔ159 include a potential endoplasmic reticulum (ER) retention signal, RGR, which when mutated to LGL (HERGΔ147-LGL) restored IKr. Streptavidin selection of biotin-labeled surface proteins showed good expression of wild-type and HERGΔ159 at the cell surface and low expression of HERGΔ147-LGL and HERGΔ147. Additionally, a 100-amino acid peptide spanning the RGR triplet can rescue the defect in HERGΔ147 when co-expressed as an ER-targeted minigene. Failure of HERG trafficking is known to cause LQT2, and this identified a molecular mechanism underlying this defect. Further, our data indicate that a key function of the C-terminal 104 amino acids is to mask the RGR ER retention signal, which becomes exposed when mutations truncate the HERG C terminus.
Kupershmidt et al. (Mon,) conducted a other in Long QT syndrome (LQT2). HERG C-terminal deletions and mutations vs. Wild-type HERG was evaluated on I_Kr current amplitude and surface protein expression. Deletion of the HERG C-terminal 147 amino acids exposes an RGR endoplasmic reticulum retention signal that abolishes I_Kr current by preventing protein trafficking to the cell surface.