Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan 48109, United States.
McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States.
Biochemistry. 2023 Apr 18;62(8):1331-1336. doi: 10.1021/acs.biochem.3c00026. Epub 2023 Apr 4.
Myoregulin (MLN) is a member of the regulin family, a group of homologous membrane proteins that bind to and regulate the activity of the sarcoplasmic reticulum Ca-ATPase (SERCA). MLN, which is expressed in skeletal muscle, contains an acidic residue in its transmembrane domain. The location of this residue, Asp35, is unusual because the relative occurrence of aspartate is very rare (<0.2%) within the transmembrane helix regions. Therefore, we used atomistic simulations and ATPase activity assays of protein co-reconstitutions to probe the functional role of MLN residue Asp35. These structural and functional studies showed Asp35 has no effects on SERCA's affinity for Ca or the structural integrity of MLN in the lipid bilayer. Instead, Asp35 controls SERCA inhibition by populating a bound-like orientation of MLN. We propose Asp35 provides a functional advantage over other members of the regulin family by populating preexisting MLN conformations required for MLN-specific regulation of SERCA. Overall, this study provides new clues about the evolution and functional divergence of the regulin family and offers novel insights into the functional role of acidic residues in transmembrane protein domains.
肌联蛋白 (MLN) 是调节蛋白家族的成员之一，该家族是一组同源的膜蛋白，可结合并调节肌浆网 Ca-ATP 酶 (SERCA) 的活性。MLN 在骨骼肌中表达，其跨膜结构域含有一个酸性残基。该残基天冬氨酸 (Asp35) 的位置很不寻常，因为天冬氨酸的相对出现频率在跨膜螺旋区域非常低（<0.2%）。因此，我们使用原子模拟和蛋白质共重建的 ATP 酶活性测定来探究 MLN 残基 Asp35 的功能作用。这些结构和功能研究表明，Asp35 对 SERCA 与 Ca 的亲和力或 MLN 在脂质双层中的结构完整性没有影响。相反，Asp35 通过占据类似于结合的 MLN 构象来控制 SERCA 的抑制。我们提出，Asp35 通过占据 MLN 特有的 SERCA 调节所需的现有 MLN 构象，为调节蛋白家族提供了比其他成员更具功能性的优势。总的来说，这项研究为调节蛋白家族的进化和功能分化提供了新的线索，并为跨膜蛋白结构域中酸性残基的功能作用提供了新的见解。
