An Eag Domain Polypeptide Regulates the Deactivation Kinetics of the hERG 1A-3.1 Splice Variant Linked to Schizophrenia

Abstract

The Human Ether-a-go-go Related Gene (hERG) encodes a voltage-activated K+ channel. hERG contributes to the repolarization of the ventricular action potential as the primary component of the cardiac delayed rectifier K+ current (IKr) and has also been shown by many groups to modulate neuronal firing frequency. Disruption of channel function by inherited mutations in the gene encoding hERG has been shown to cause type 2 long QT syndrome (LQT2). hERG gating is characterized by rapid inactivation upon depolarization and rapid recovery from inactivation and slow closing (deactivation) upon repolarization. Unlike other K+ channels, hERG, ELK and EAG channels contain an N-terminal eag domain, composed of a PAS domain and a PAS-Cap domain in the N-terminal region. Inter-subunit interactions between the N-terminal eag domain and the C-terminal cyclic-nucleotide binding homology domain regulate slow deactivation kinetics in the original variant of hERG, hERG1a channels. A recently discovered splice variant, hERG 1a-3.1, has much faster deactivation and has been linked to schizophrenia. We demonstrate in HEK293 cells, that co-expression of hERG1a-3.1 with soluble eag domain peptide partially rescues deactivation kinetics, presumably by providing a fully functional eag domain to the eag-truncated hERG1a-3.1 to slow channel deactivation. Cells co-expressing hERG1a-3.1 + eag domain polypeptides had significantly slower fast and slow time constants of deactivation compared to hERG1a-3.1 channels alone (p<0.05). We conclude that eag domain polypeptides are able to partially restore deactivation gating. Current experiments are utilizing FRET to assess if the hERG1a-3.1 C-terminus interaction with the eag domain is physically disrupted.