The intracellular segment of the sodium channel beta 1 subunit is required for its efficient association with the channel alpha subunit.
Sodium channels consist of a pore-forming alpha subunit and auxiliary beta 1 and beta 2 subunits. The subunit beta 1 alters the kinetics and voltage-dependence of sodium channels expressed in Xenopus oocytes or mammalian cells. Functional modulation in oocytes depends on specific regions in the N-terminal extracellular domain of beta 1, but does not require the intracellular C-terminal domain. Functional modulation is qualitatively different in mammalian cells, and thus could involve different molecular mechanisms. As a first step toward testing this hypothesis, we examined modulation of brain Na(V)1.2a sodium channel alpha subunits expressed in Chinese hamster lung cells by a mutant beta1 construct with 34 amino acids deleted from the C-terminus. This deletion mutation did not modulate sodium channel function in this cell system. Co-immunoprecipitation data suggest that this loss of functional modulation was caused by inefficient association of the mutant beta 1 with alpha, despite high levels of expression of the mutant protein. In Xenopus oocytes, injection of approximately 10,000 times more mutant beta 1 RNA was required to achieve the level of functional modulation observed with injection of full-length beta 1. Together, these findings suggest that the C-terminal cytoplasmic domain of beta 1 is an important determinant of beta1 binding to the sodium channel alpha subunit in both mammalian cells and Xenopus oocytes.
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
L
L
Meadows
J D
JD
Malhotra
A
A
Stetzer
L L
LL
Isom
D S
DS
Ragsdale
D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D008322:Mammals; D008564:Membrane Potentials; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D021122:Protein Subunits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012530:Saxitoxin / Q000493:pharmacokinetics; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis
D021122:Protein Subunits; D011994:Recombinant Proteins; D015222:Sodium Channels; D012530:Saxitoxin