Department of Biochemistry, University of Alberta, Edmonton, Canada.
Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, United States.
Elife. 2021 Jun 2;10:e65545. doi: 10.7554/eLife.65545.
The sarco-plasmic reticulum calcium pump (SERCA) plays a critical role in the contraction-relaxation cycle of muscle. In cardiac muscle, SERCA is regulated by the inhibitor phospholamban. A new regulator, dwarf open reading frame (DWORF), has been reported to displace phospholamban from SERCA. Here, we show that DWORF is a direct activator of SERCA, increasing its turnover rate in the absence of phospholamban. Measurement of in-cell calcium dynamics supports this observation and demonstrates that DWORF increases SERCA-dependent calcium reuptake. These functional observations reveal opposing effects of DWORF activation and phospholamban inhibition of SERCA. To gain mechanistic insight into SERCA activation, fluorescence resonance energy transfer experiments revealed that DWORF has a higher affinity for SERCA in the presence of calcium. Molecular modeling and molecular dynamics simulations provide a model for DWORF activation of SERCA, where DWORF modulates the membrane bilayer and stabilizes the conformations of SERCA that predominate during elevated cytosolic calcium.
肌浆网钙泵（SERCA）在肌肉的收缩-舒张循环中起着关键作用。在心肌中，SERCA 受抑制剂磷酸化酶调节。据报道，一种新的调节剂，矮小开放阅读框（DWORF），可以将磷酸化酶从 SERCA 上置换下来。在这里，我们表明 DWORF 是 SERCA 的直接激活剂，在没有磷酸化酶的情况下增加其周转率。细胞内钙动力学的测量支持了这一观察结果，并表明 DWORF 增加了 SERCA 依赖性钙摄取。这些功能观察揭示了 DWORF 激活和磷酸化酶抑制 SERCA 的相反作用。为了深入了解 SERCA 的激活机制，荧光共振能量转移实验表明，DWORF 在钙存在的情况下对 SERCA 具有更高的亲和力。分子建模和分子动力学模拟为 SERCA 的 DWORF 激活提供了一个模型，其中 DWORF 调节膜双层并稳定 SERCA 的构象，这些构象在细胞溶质钙升高时占主导地位。
