Oligomeric properties of .alpha.-dendrotoxin-sensitive potassium ion channels purified from bovine brain

Abstract

Neuronal acceptors for alpha-dendrotoxin (alpha-DTX) have recently been purified from mammalian brain and shown to consist of two classes of subunit, a larger (approximately 78,000 M(r)) protein (alpha) whose N-terminal sequence is identical to that of a cloned, alpha-DTX-sensitive K+ channel, and a novel M(r) 39,000 (beta) polypeptide of unknown function. However, little information is available regarding the oligomeric composition of these native molecules. By sedimentation analysis of alpha-DTX acceptors isolated from bovine cortex, two species have been identified. A minority of these oligomers contain only the larger protein, while the vast majority possess both subunits. Based on accurate determination of the molecular weights of these two forms it is proposed that alpha-DTX-sensitive K+ channels exist as alpha 4 beta 4 complexes because this combination gives the best fit to the experimental data.

Fluorescence measurements reveal stoichiometry of K + channels formed by modulatory and delayed rectifier α-subunits

“…A diverse set of intracellular and transmembrane auxiliary subunits has evolved to regulate these gating transitions and tune native Kv channels to tissue-specific requirements (1). A consistent observation so far is that an even number of pore-forming ␣-subunits and auxiliary subunits assemble into symmetric Kv channel complexes (2)(3)(4)(5). Modulatory ␣-subunits combine features of both auxiliary proteins and ␣-subunits and comprise the largest group of mammalian K ϩ channel-regulating proteins so far described, consisting of Kv5.1, Kv6.1-6.4, Kv8.1-8.2, and Kv9.1-9.3 subunits (6)(7)(8)(9)(10)(11)(12).…”

“…Here, we report the assembly of the modulatory ␣-subunit Kv9.3 with Kv2.1 into functional channels consisting of three Kv2.1 subunits and one Kv9.3 subunit. For K ϩ channels, which have been a beacon of molecular symmetry, this finding stands out from a crowd of heteromeric K ϩ channels formed by different nonmodulatory ␣-subunits (30,31) and assemblies of ␣-subunit tetramers with transmembrane or intracellular auxiliary proteins reported to result in symmetric complexes with even-numbered stoichiometries (2)(3)(4)(5).…”

The role of humoral autoimmunity in gastrointestinal neuromuscular diseases

“…However, due to the assembly of heteromultimeric channels (MacKinnon 1991;Parcej et al 1992) and the heterogeny of diseases associated with anti-VGKC autoimmunity (Rueff et al 2008), it is likely that other members of this subfamily also have pathogenic importance. Therefore, we investigated the expression of Epithelial K V 1 channel subunit expression varied according to the region studied.…”

Substrate profiling and aldehyde dismutase activity of the Kvβ2 subunit of the mammalian Kv1 potassium channel

“…Four voltage sensing, integral membrane pore-forming Kvα subunits assemble to form the Shaker-related voltage-gated K + channels (Kv1 subfamily) (Kolb, 1990;Orlova et al, 2003). The auxillary β-subunit, Kvβ2, associated with the cytoplasmic face of Kvα proteins (Dolly et al, 1994;Parcej et al, 1992;Scott et al, 1994), has a conserved catalytic core that shows a high level of sequence homology with aldo-keto reductase (AKR) enzymes (Gulbis et al, 1999;Long et al, 2005). The catalytic C-terminal of Kvβ2 has a tightly, but non-covalently, bound nicotinamide (NADPH) cofactor and an aldehyde binding site.…”