βSubunits Promote K+ Channel Surface Expression through Effects Early in Biosynthesis

Abstract

Voltage-gated K+ channels are protein complexes composed of ion-conducting integral membrane alpha subunits and cytoplasmic beta subunits. Here, we show that, in transfected mammalian cells, the predominant beta subunit isoform in brain, Kv beta 2, associates with the Kv1.2 alpha subunit early in channel biosynthesis and that Kv beta 2 exerts multiple chaperone-like effects on associated Kv1.2 including promotion of cotranslational N-linked glycosylation of the nascent Kv1.2 polypeptide, increased stability of Kv beta 2/Kv1.2 complexes, and increased efficiency of cell surface expression of Kv1.2. Taken together, these results indicate that while some cytoplasmic K+ channel beta subunits affect the inactivation kinetics of alpha subunits, a more general, and perhaps more fundamental, role is to mediate the biosynthetic maturation and surface expression of voltage-gated K+ channel complexes. These findings provide a molecular basis for recent genetic studies indicating that beta subunits are key determinants of neuronal excitability.

sup-9, sup-10, andunc-93May Encode Components of a Two-Pore K+Channel that Coordinates Muscle Contraction inCaenorhabditis elegans

“…The cytoplasmic regulatory subunit K v ␤2 associates with Shaker-like K v channels and increases their surface expression in heterologous systems (Shi et al, 1996) while exerting small effects on channel activity (Rettig et al, 1994;Heinemann et al, 1996). In addition to regulating K ϩ channels through chaperone activity or altering gating kinetics, some channel subunits, such as the SUR1 subunit of K ir 6.2 channels or the ␤1 subunits of Slo channels, alter the sensitivities of their associated channels to activating signals, such as voltage, ATP, or Ca 2ϩ (McManus et al, 1995;Tucker et al, 1997).…”

Trafficking-dependent phosphorylation of Kv1.2 regulates voltage-gated potassium channel cell surface expression

“…1 A) (17). The low M r form corresponds to the newly synthesized ER-localized pool of Kv1.2, whereas the high M r form is found in the Golgi apparatus and on the cell surface (12,13). Because virtually all of the low and high M r forms are in the ER and on the cell surface, respectively (12), for simplicity we will refer to the two pools hereafter as ''ER'' and ''cell surface.''…”

“…As a first step toward characterizing Kv1.2 phosphorylation, we subjected endogenous Kv1.2 in crude rat brain membranes (RBM) and recombinant rat Kv1.2 expressed in HEK293 cells to digestion with alkaline phosphatase (AP). Kv1.2 was expressed in HEK293 cells without and with auxiliary Kv␤2 subunits to alter the relative proportions of ER and cell-surface pools (13)(14)(15). The high M r cell-surface form of both native brain Kv1.2 and recombinant Kv1.2 from HEK293 cells underwent large shifts in M r upon AP treatment ( Fig.…”

Effects ofHyperkinetic, a β Subunit ofShakerVoltage-Dependent K+Channels, on the Oxidation State of Presynaptic Nerve Terminals

“…These β subunits attach to the cytosolic face of their α subunit counterparts encoded by Shaker (Sh) and its vertebrate homologs, Kv1 channel genes (Sewing et al, 1996;Yu et al, 1996;Long et al, 2005). Physical interaction between the two subunits determines activation-inactivation kinetics, voltage sensitivity (Rettig et al, 1994;Chouinard et al, 1995), and surface expression (Shi et al, 1996;Accili et al, 1997) of these inactivating I A channels. Disruptions of the Hk gene in Drosophila slows down the kinetics and decreases the voltage sensitivity of Sh currents in larval muscles (Wang & Wu, 1996).…”