Structural Biology Group, Max-Planck-Institute for Molecular Physiology, Dortmund, Germany.
EMBO J. 2011 Aug 16;30(20):4185-97. doi: 10.1038/emboj.2011.291.
The bacterium Myxococcus xanthus uses a G protein cycle to dynamically regulate the leading/lagging pole polarity axis. The G protein MglA is regulated by its GTPase-activating protein (GAP) MglB, thus resembling Ras family proteins. Here, we show structurally and biochemically that MglA undergoes a dramatic, GDP-GTP-dependent conformational change involving a screw-type forward movement of the central β2-strand, never observed in any other G protein. This movement and complex formation with MglB repositions the conserved residues Arg53 and Gln82 into the active site. Residues required for catalysis are thus not provided by the GAP MglB, but by MglA itself. MglB is a Roadblock/LC7 protein and functions as a dimer to stimulate GTP hydrolysis in a 2:1 complex with MglA. In vivo analyses demonstrate that hydrolysis mutants abrogate Myxococcus' ability to regulate its polarity axis changing the reversal behaviour from stochastic to oscillatory and that both MglA GTPase activity and MglB GAP catalysis are essential for maintaining a proper polarity axis.
粘细菌 Myxococcus xanthus 利用 G 蛋白循环来动态调节领先/滞后极极性轴。G 蛋白 MglA 受其 GTP 酶激活蛋白（GAP）MglB 调节，因此类似于 Ras 家族蛋白。在这里，我们从结构和生化角度表明，MglA 发生了剧烈的、依赖 GDP-GTP 的构象变化，涉及中央 β2-链的螺旋式向前运动，这在任何其他 G 蛋白中都从未观察到过。这种运动和与 MglB 的复合重新定位了保守残基 Arg53 和 Gln82 到活性位点。因此，催化所需的残基不是由 GAP MglB 提供，而是由 MglA 本身提供。MglB 是 Roadblock/LC7 蛋白，作为二聚体发挥作用，以刺激 MglA 形成 2:1 复合物中的 GTP 水解。体内分析表明，水解突变体使粘细菌失去调节其极性轴的能力，使反转行为从随机变为振荡，并且 MglA GTP 酶活性和 MglB GAP 催化对于维持适当的极性轴都是必不可少的。
