TY - JOUR
T1 - Translocatable voltage-gated Ca2+ channel β subunits in α1-β complexes reveal competitive replacement yet no spontaneous dissociation
AU - Yeon, Jun Hee
AU - Park, Cheon Gyu
AU - Hille, Bertil
AU - Suh, Byung Chang
N1 - Publisher Copyright:
© 2018 National Academy of Sciences. All Rights Reserved.
PY - 2018/10/16
Y1 - 2018/10/16
N2 - β subunits of high voltage-gated Ca2+ (CaV) channels promote cellsurface expression of pore-forming α1 subunits and regulate channel gating through binding to the α-interaction domain (AID) in the first intracellular loop. We addressed the stability of CaV α1B-β interactions by rapamycin-translocatable CaV β subunits that allow drug-induced sequestration and uncoupling of the β subunit from CaV2.2 channel complexes in intact cells. Without CaV α1B/α2δ1, all modified β subunits, except membrane-tethered β2a and β2e, are in the cytosol and rapidly translocate upon rapamycin addition to anchors on target organelles: Plasma membrane, mitochondria, or endoplasmic reticulum. In cells coexpressing CaV α1B/α2δ1 subunits, the translocatable β subunits colocalize at the plasma membrane with α1B and stay there after rapamycin application, indicating that interactions between α1B and bound β subunits are very stable. However, the interaction becomes dynamic when other competing β isoforms are coexpressed. Addition of rapamycin, then, switches channel gating and regulation by phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] lipid. Thus, expression of free β isoforms around the channel reveals a dynamic aspect to the α1B-β interaction. On the other hand, translocatable β subunits with AID-binding site mutations are easily dissociated from CaV α1B on the addition of rapamycin, decreasing current amplitude and PI(4,5)P2 sensitivity. Furthermore, the mutations slow CaV2.2 current inactivation and shift the voltage dependence of activation to more positive potentials. Mutated translocatable β subunits work similarly in CaV2.3 channels. In sum, the strong interaction of CaV α1B-β subunits can be overcome by other free β isoforms, permitting dynamic changes in channel properties in intact cells.
AB - β subunits of high voltage-gated Ca2+ (CaV) channels promote cellsurface expression of pore-forming α1 subunits and regulate channel gating through binding to the α-interaction domain (AID) in the first intracellular loop. We addressed the stability of CaV α1B-β interactions by rapamycin-translocatable CaV β subunits that allow drug-induced sequestration and uncoupling of the β subunit from CaV2.2 channel complexes in intact cells. Without CaV α1B/α2δ1, all modified β subunits, except membrane-tethered β2a and β2e, are in the cytosol and rapidly translocate upon rapamycin addition to anchors on target organelles: Plasma membrane, mitochondria, or endoplasmic reticulum. In cells coexpressing CaV α1B/α2δ1 subunits, the translocatable β subunits colocalize at the plasma membrane with α1B and stay there after rapamycin application, indicating that interactions between α1B and bound β subunits are very stable. However, the interaction becomes dynamic when other competing β isoforms are coexpressed. Addition of rapamycin, then, switches channel gating and regulation by phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] lipid. Thus, expression of free β isoforms around the channel reveals a dynamic aspect to the α1B-β interaction. On the other hand, translocatable β subunits with AID-binding site mutations are easily dissociated from CaV α1B on the addition of rapamycin, decreasing current amplitude and PI(4,5)P2 sensitivity. Furthermore, the mutations slow CaV2.2 current inactivation and shift the voltage dependence of activation to more positive potentials. Mutated translocatable β subunits work similarly in CaV2.3 channels. In sum, the strong interaction of CaV α1B-β subunits can be overcome by other free β isoforms, permitting dynamic changes in channel properties in intact cells.
KW - CaVβ subunits
KW - Chemically inducible dimerization
KW - PI(4,5)P
KW - Rapamycin
KW - Voltage-gated Ca channel
UR - http://www.scopus.com/inward/record.url?scp=85054952846&partnerID=8YFLogxK
U2 - 10.1073/pnas.1809762115
DO - 10.1073/pnas.1809762115
M3 - Article
C2 - 30257950
AN - SCOPUS:85054952846
SN - 0027-8424
VL - 115
SP - E9934-E9943
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 42
ER -