MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH Scotland, UK.
Biochem Biophys Res Commun. 2013 Feb 15;431(3):604-9. doi: 10.1016/j.bbrc.2012.12.113. Epub 2013 Jan 4.
The MO25 scaffolding protein operates as critical regulator of a number of STE20 family protein kinases (e.g. MST and SPAK isoforms) as well as pseudokinases (e.g. STRAD isoforms that play a critical role in activating the LKB1 tumour suppressor). To better understand how MO25 interacts and stimulates the activity of STE20 protein kinases, we determined the crystal structure of MST3 catalytic domain (residues 19-289) in complex with full length MO25β. The structure reveals an intricate web of interactions between MST3 and MO25β that function to stabilise the kinase domain in a closed, active, conformation even in the absence of ATP or an ATP-mimetic inhibitor. The binding mode of MO25β is reminiscent of the mechanism by which MO25α interacts with the pseudokinase STRADα. In particular we identified interface residues Tyr223 of MO25β and Glu58 and Ile71 of MST3 that when mutated prevent activation of MST3 by MO25β. These data provide molecular understanding of the mechanism by which MO25 isoforms regulates the activity of STE20 family protein kinases.
MO25 支架蛋白作为许多 STE20 家族蛋白激酶（例如 MST 和 SPAK 同工型）以及拟激酶（例如在激活 LKB1 肿瘤抑制因子中起关键作用的 STRAD 同工型）的关键调节剂发挥作用。为了更好地了解 MO25 如何相互作用并刺激 STE20 蛋白激酶的活性，我们确定了全长 MO25β 与 MST3 催化结构域（残基 19-289）复合物的晶体结构。该结构揭示了 MST3 和 MO25β 之间错综复杂的相互作用网络，即使在没有 ATP 或 ATP 模拟抑制剂的情况下，该网络也能稳定激酶结构域处于封闭、活跃的构象。MO25β 的结合模式让人联想到 MO25α 与伪激酶 STRADα 相互作用的机制。特别是，我们确定了 MO25β 的 Tyr223 和 MST3 的 Glu58 和 Ile71 界面残基，当这些残基发生突变时，会阻止 MO25β 激活 MST3。这些数据提供了对 MO25 同工型调节 STE20 家族蛋白激酶活性的机制的分子理解。
