BPS2026 – Structural insights into small molecule- and peptide-mediated activation of the cardiac Ca2+ pump, SERCA

The carefully coordinated contraction-relaxation cycle of cardiomyocytes is critical for maintaining heart function. Muscle relaxation relies on the sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA), which restores cytosolic Ca 2+ to the sarcoplasmic reticulum (SR) lumen. SERCA activity is modulated by small transmembrane peptide regulators, termed regulins, which directly interact with and alter its Ca 2+ transport properties. The only known peptide activator, DWORF (dwarf open reading frame), enhances SERCA function and ATP-dependent Ca 2+ transport. Impaired SR Ca 2+ refilling is strongly linked to heart failure, highlighting SERCA activation as a promising therapeutic target. The small molecules CDN1163 and compound 52, allosteric SERCA activators, have been shown to have potential to restore Ca 2+ homeostasis, yet their binding site and biochemical interplay with DWORF remain unresolved. Here, we employed cryo-electron microscopy (cryo-EM) and in vitro biochemical assays to define the molecular basis of CDN1163, compound 5911, and DWORF-mediated SERCA activation. We reconstructed SERCA in the presence of CDN1163 to near-atomic resolution (2.7 Å, GSFSC) and in the presence of compound 52 (3.1 Å, GSFSC). These findings not only identify the binding site for CDN1163 and compound 52 but also inform the design of small-molecule and peptide-based biologics for therapeutic intervention in cardiomyopathy.