Functional dissection of the intramolecular Src homology 3‐guanylate kinase domain coupling in voltage‐gated Ca2+ channel β‐subunits

The β‐subunit of voltage‐gated Ca2+ channels is essential for trafficking the channels to the plasma membrane and regulating their gating. It contains a Src homology 3 (SH3) domain and a guanylate kinase (GK) domain, which interact intramolecularly. We investigated the structural underpinnings of this intramolecular coupling and found that in addition to a previously described SH3 domain β strand, two structural elements are crucial for maintaining a strong and yet potentially modifiable SH3–GK intramolecular coupling: an intrinsically weak SH3–GK interface and a direct connection of the SH3 and GK domains. Alterations of these elements uncouple the two functions of the β‐subunit, degrading its ability to regulate gating while leaving its chaperone effect intact.