Question: 

The product of the gene which leads to Best's vitelliforme macular degeneration, bestrophin-1, can function as regulator of voltage-dependent L-type Ca²⁺ channels. Mice deficient for either b4-subunits or Ca_V1.3 subunits show reduced light-peaks, the main symptom of Best's disease.

Methods/Results: 

We studied binding and localization of bestrophin-1 and Ca²⁺ channel subunits together with modulation of Ca_V1.3 Ca²⁺ channels currents by heterologous expression of full length bestrophin-1, b4-subunit and the pore forming Ca_V1.3 subunit. Precipitation of b4-subunits leads to co-precipitation with bestrophin-1. Analysis of subcellular localization showed co-localization of bestrophin-1, Ca_V1.3 and b4-subunit in the cell membrane. Ca_V1.3 currents in the presence of b4-subunits and bestrophin-1 showed accelerated time-dependent activation and decreased current density compared to currents measured in the absence of bestrophin-1. Deletion of a cluster of proline-rich motifs (either 330 and 346 or 468 and 486) on the C-terminus of bestrophin-1 reduced co-immuno precipitation of b4-subunit with bestrophin-1 and strongly reduced the Ca_V1.3 activity, but still showed faster activation. Cells which co-express bestrophin-1 lacking one of these clusters of proline-rich motifs and Ca_V1.3 subunits showed that both proteins traveled less efficiently into the cell membrane.

Conclusion: 

In summary we conclude that bestrophin-1 modulates L-type channels via proline-rich motif-dependent interaction with b4-subunits. A disturbed interaction reduces the presence of Ca_V1.3 subunits in the cell membrane. Thus this study could help to understand changes in the patient's electro-oculogram and functional alterations of the RPE leading to retinal degeneration. Furthermore we identified new proline-rich motifs for interaction with Ca²⁺ channel b-subunits.