Phosphorylation of Ser272 and Ser300 in Rad's C-terminal domain causes its dissociation from the sarcolemma and CaVβ, enabling sympathetic upregulation of cardiac calcium currents.
Dissociation of the small G protein Rad from the sarcolemma via phosphorylation of its C-terminal domain is the primary mechanism for sympathetic upregulation of cardiac calcium currents.
The ability to fight or flee from a threat relies on an acute adrenergic surge that augments cardiac output, which is dependent on increased cardiac contractility and heart rate. This cardiac response depends on β-adrenergic-initiated reversal of the small RGK G protein Rad-mediated inhibition of voltage-gated calcium channels (CaV) acting through the Cavβ subunit. Here, we investigate how Rad couples phosphorylation to augmented Ca2+ influx and increased cardiac contraction. We show that reversal required phosphorylation of Ser272 and Ser300 within Rad's polybasic, hydrophobic C-terminal domain (CTD). Phosphorylation of Ser25 and Ser38 in Rad's N-terminal domain (NTD) alone was ineffective. Phosphorylation of Ser272 and Ser300 or the addition of 4 Asp residues to the CTD reduced Rad's association with the negatively charged, cytoplasmic plasmalemmal surface and with CaVβ, even in the absence of CaVα, measured here by FRET. Addition of a posttranslationally prenylated CAAX motif to Rad's C-terminus, which constitutively tethers Rad to the membrane, prevented the physiological and biochemical effects of both phosphorylation and Asp substitution. Thus, dissociation of Rad from the sarcolemma, and consequently from CaVβ, is sufficient for sympathetic upregulation of Ca2+ currents.
Papa et al. (2024) studied Cardiac calcium channel regulation. Rad phosphorylation (Ser272 and Ser300) was evaluated on Rad association with plasmalemmal surface and CaVβ. Phosphorylation of Ser272 and Ser300 in Rad's C-terminal domain causes its dissociation from the sarcolemma and CaVβ, enabling sympathetic upregulation of cardiac calcium currents.