A novel integral voltage sensor-interacting protein: Shedding light on the gating mechanisms of somatodendritic Kv channels
Members of the Kv4 family of voltage-gated K+ channels mediate the somatodendritic A-type current (ISA) in neurons. The ISA has been shown to control several aspects of dendritic integration, including the attenuation of back-propagating action potentials, the maintenance of slow repetitive firing, and the electrical sequestration of neighboring dendritic branches. In neurons, Kv4 channels exist as oligomeric complexes comprised of the Kv4 channel α-subunit and two distinct classes of β-subunits; K+ Channel-Interacting Proteins (KChIPs) and Dipeptidyl aminoPeptidase-Like Proteins (DPLPs). Kv4 channels interact with KChIP β-subunits, which are small cytoplasmic Ca2+ binding proteins, through their N-terminus and cytoplasmic Ti domain resulting in a distinct inactivation phenotype. This interaction has been extensively characterized. The interaction between Kv4 channels and DPLPs, which, in contrast with KChIP1 are type-II transmembrane proteins, remains poorly understood. DPLPs primarily remodel the biophysical profile of Kv4 channels. The best characterized DPLP, DPPX-S, shifts the Gp-V relationship by ∼ -25 mV and accelerates macroscopic inactivation and recovery from inactivation when coexpressed with Kv4.2 channels. However, our understanding of this interaction remains vague. In this work, we thoroughly investigate the interaction between Kv4.2 and DPPX-S using heterologous expression in tsA201 cells, patch-clamp electrophysiology, and in vitro translation biochemistry. Briefly, we discovered that DPPX-S remodels the movement of the gating charge in Kv4.2 channels through a direct interaction with the Kv4.2 voltage-sensing domain. We also investigated the influence of DPPX-S over closed-state inactivation in Kv4.2 channels and propose a tenable mechanism for the effect of DPPX-S on inactivation in Kv4.2 channels. In all, this work dramatically enhances our understanding of both the fundamentals of gating charge movement in Kv4.2 channels and the interaction between Kv4.2 and its obligate neuronal β-subunit DPPX-S.