Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany.
Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany
Proc Natl Acad Sci U S A. 2020 Sep 22;117(38):23859-23868. doi: 10.1073/pnas.2004722117. Epub 2020 Sep 8.
Bacteria can move across surfaces using type IV pili (T4P), which undergo cycles of extension, adhesion, and retraction. The T4P localization pattern varies between species; however, the underlying mechanisms are largely unknown. In the rod-shaped cells, T4P localize at the leading cell pole. As cells reverse their direction of movement, T4P are disassembled at the old leading pole and then form at the new leading pole. Thus, cells can form T4P at both poles but engage only one pole at a time in T4P formation. Here, we address how this T4P unipolarity is realized. We demonstrate that the small Ras-like GTPase MglA stimulates T4P formation in its GTP-bound state by direct interaction with the tetratricopeptide repeat (TPR) domain-containing protein SgmX. SgmX, in turn, is important for polar localization of the T4P extension ATPase PilB. The cognate MglA GTPase activating protein (GAP) MglB, which localizes mainly to the lagging cell pole, indirectly blocks T4P formation at this pole by stimulating the conversion of MglA-GTP to MglA-GDP. Based on these findings, we propose a model whereby T4P unipolarity is accomplished by stimulation of T4P formation at the leading pole by MglA-GTP and SgmX and indirect inhibition of T4P formation at the lagging pole by MglB due to its MglA GAP activity. During reversals, MglA, SgmX, and MglB switch polarity, thus laying the foundation for T4P formation at the new leading pole and inhibition of T4P formation at the new lagging pole.
细菌可以使用 IV 型菌毛（T4P）在表面上移动，T4P 经历延伸、粘附和缩回的循环。T4P 的定位模式在物种之间有所不同；然而，其潜在机制在很大程度上尚不清楚。在杆状细胞中，T4P 定位于细胞的前极。当细胞改变运动方向时，T4P 在旧的前极处解体，然后在前新的前极处形成。因此，细胞可以在前极和新的前极都形成 T4P，但一次只在前极形成 T4P。在这里，我们解决了这种 T4P 单极性是如何实现的。我们证明，小 Ras 样 GTPase MglA 通过与包含四肽重复（TPR）结构域的蛋白质 SgmX 的直接相互作用，在其 GTP 结合状态下刺激 T4P 的形成。反过来，SgmX 对于 T4P 延伸 ATP 酶 PilB 的极性定位很重要。同源的 MglA GTPase 激活蛋白（GAP）MglB 主要定位于滞后细胞极，通过刺激 MglA-GTP 向 MglA-GDP 的转化，间接阻止该极的 T4P 形成。基于这些发现，我们提出了一个模型，即通过 MglA-GTP 和 SgmX 刺激前极的 T4P 形成以及 MglB 通过其 MglA GAP 活性间接抑制滞后极的 T4P 形成来实现 T4P 单极性。在反转过程中，MglA、SgmX 和 MglB 切换极性，从而为新的前极的 T4P 形成和新的滞后极的 T4P 形成抑制奠定了基础。
