Disruption of the Key Ca2+ Binding Site in the Selectivity Filter of Neuronal Voltage-Gated Calcium Channels Inhibits Channel Trafficking

摘要

Voltage-gated calcium channels are exquisitely Casup2+/sup selective, conferred primarily by four conserved pore-loop glutamate residues contributing to the selectivity filter. There has been little previous work directly measuring whether the trafficking of calcium channels requires their ability to bind Casup2+/sup in the selectivity filter or to conduct Casup2+/sup. Here, we examine trafficking of neuronal CasubV/sub2.1 and 2.2 channels with mutations in their selectivity filter and find reduced trafficking to the cell surface in cell lines. Furthermore, in hippocampal neurons, there is reduced trafficking to the somatic plasma membrane, into neurites, and to presynaptic terminals. However, the CasubV/sub2.2 selectivity filter mutants are still influenced by auxiliary αsub2/subδ subunits and, albeit to a reduced extent, by β subunits, indicating the channels are not grossly misfolded. Our results indicate that Casup2+/sup binding in the pore of CasubV/sub2 channels may promote their correct trafficking, in combination with auxiliary subunits. Furthermore, physiological studies utilizing selectivity filter mutant CasubV/sub channels should be interpreted with caution.