β Subunit Heterogeneity in N-type Ca2+ Channels

The β subunit of the voltage-dependent Ca2+ channel is a cytoplasmic protein that interacts directly with an α1 subunit, thereby modulating the biophysical properties of the channel. Herein, we demonstrate that the α1B subunit of the N-type Ca2+ channel associates with several different β subunits. Polyclonal antibodies specific for three different β subunits immunoprecipitated 125I-ω-conotoxin GVIA binding from solubilized rabbit brain membranes. Enrichment of the N-type Ca2+ channels with an α1B subunit-specific monoclonal antibody showed the association of β1b, β3, and β4 subunits. Protein sequencing of tryptic peptides of the 57-kDa component of the purified N-type Ca2+ channel confirmed the presence of the β3 and β4 subunits. Each of the β subunits bound to the α1B subunit interaction domain with similar high affinity. Thus, our data demonstrate important heterogeneity in the β subunit composition of the N-type Ca2+ channels, which may be responsible for some of the diverse kinetic properties recorded from neurons. The β subunit of the voltage-dependent Ca2+ channel is a cytoplasmic protein that interacts directly with an α1 subunit, thereby modulating the biophysical properties of the channel. Herein, we demonstrate that the α1B subunit of the N-type Ca2+ channel associates with several different β subunits. Polyclonal antibodies specific for three different β subunits immunoprecipitated 125I-ω-conotoxin GVIA binding from solubilized rabbit brain membranes. Enrichment of the N-type Ca2+ channels with an α1B subunit-specific monoclonal antibody showed the association of β1b, β3, and β4 subunits. Protein sequencing of tryptic peptides of the 57-kDa component of the purified N-type Ca2+ channel confirmed the presence of the β3 and β4 subunits. Each of the β subunits bound to the α1B subunit interaction domain with similar high affinity. Thus, our data demonstrate important heterogeneity in the β subunit composition of the N-type Ca2+ channels, which may be responsible for some of the diverse kinetic properties recorded from neurons.