Department of Human Biology, Faculty of Natural Science, University of Haifa, Haifa 3498838, Israel.
Department of Human Biology, Faculty of Natural Science, University of Haifa, Haifa 3498838, Israel
Biochem J. 2018 Jul 26;475(14):2293-2304. doi: 10.1042/BCJ20180285.
Regulators of G protein signaling (RGS) proteins inactivate Gα subunits, thereby controlling G protein-coupled signaling networks. Among all RGS proteins, RGS2 is unique in interacting only with the Gα but not with the Gα subfamily. Previous studies suggested that this specificity is determined by the RGS domain and, in particular, by three RGS2-specific residues that lead to a unique mode of interaction with Gα This interaction was further proposed to act through contacts with the Gα GTPase domain. Here, we combined energy calculations and GTPase activity measurements to determine which Gα residues dictate specificity toward RGS2. We identified putative specificity-determining residues in the Gα helical domain, which among G proteins is found only in Gα subunits. Replacing these helical domain residues in Gα with their Gα counterparts resulted in a dramatic specificity switch toward RGS2. We further show that Gα-RGS2 specificity is set by Gα residues that perturb interactions with RGS2, and by Gα residues that enhance these interactions. These results show, for the first time, that the Gα helical domain is central to dictating specificity toward RGS2, suggesting that this domain plays a general role in governing Gα-RGS specificity. Our insights provide new options for manipulating RGS-G protein interactions , for better understanding of their 'wiring' into signaling networks, and for devising novel drugs targeting such interactions.
G 蛋白信号转导调节蛋白（RGS）使 Gα 亚基失活，从而控制 G 蛋白偶联信号转导网络。在所有 RGS 蛋白中，RGS2 是唯一与 Gα 而不是 Gα 亚家族相互作用的蛋白。先前的研究表明，这种特异性是由 RGS 结构域决定的，特别是由三个 RGS2 特异性残基决定的，这些残基导致与 Gα 的独特相互作用方式。这种相互作用被进一步提出是通过与 Gα GTPase 结构域的接触来发挥作用的。在这里，我们结合能量计算和 GTPase 活性测量来确定哪些 Gα 残基决定了对 RGS2 的特异性。我们在 Gα 的螺旋结构域中确定了假定的特异性决定残基，而在 G 蛋白中，只有 Gα 亚基存在这些残基。用 Gα 的对应残基取代 Gα 中的这些螺旋结构域残基，导致对 RGS2 的特异性发生了显著的转变。我们进一步表明，Gα-RGS2 的特异性是由扰乱与 RGS2 相互作用的 Gα 残基和增强这些相互作用的 Gα 残基决定的。这些结果首次表明，Gα 螺旋结构域是决定对 RGS2 特异性的关键，这表明该结构域在调节 Gα-RGS 特异性方面起着普遍作用。我们的研究结果为操纵 RGS-G 蛋白相互作用提供了新的选择，有助于更好地理解它们在信号转导网络中的“连接”，并为针对这些相互作用设计新型药物提供了新的思路。
