Effect of Ca _vβ Subunits on Structural Organization of Ca _v1.2 Calcium Channels

Abstract

Background

Voltage-gated Ca _v1.2 calcium channels play a crucial role in Ca ²⁺ signaling. The pore-forming α _1C subunit is regulated by accessory Ca _vβ subunits, cytoplasmic proteins of various size encoded by four different genes (Ca _vβ ₁ - β ₄) and expressed in a tissue-specific manner.

Methods and Results

Here we investigated the effect of three major Ca _vβ types, β _1b, β _2d and β ₃, on the structure of Ca _v1.2 in the plasma membrane of live cells. Total internal reflection fluorescence microscopy showed that the tendency of Ca _v1.2 to form clusters depends on the type of the Ca _vβ subunit present. The highest density of Ca _v1.2 clusters in the plasma membrane and the smallest cluster size were observed with neuronal/cardiac β _1b present. Ca _v1.2 channels containing β ₃, the predominant Ca _vβ subunit of vascular smooth muscle cells, were organized in a significantly smaller number of larger clusters. The inter- and intramolecular distances between α _1C and Ca _vβ in the plasma membrane of live cells were measured by three-color FRET microscopy. The results confirm that the proximity of Ca _v1.2 channels in the plasma membrane depends on the Ca _vβ type. The presence of different Ca _vβ subunits does not result in significant differences in the intramolecular distance between the termini of α _1C, but significantly affects the distance between the termini of neighbor α _1C subunits, which varies from 67 Å with β _1b to 79 Å with β ₃.

Conclusions

Thus, our results show that the structural organization of Ca _v1.2 channels in the plasma membrane depends on the type of Ca _vβ subunits present.