Department of Biology, University of the Pacific, Stockton, CA 95211.
Department of Biology, University of the Pacific, Stockton, CA 95211
Proc Natl Acad Sci U S A. 2021 Mar 23;118(12). doi: 10.1073/pnas.2023988118.
Motility is ubiquitous in prokaryotic organisms including the photosynthetic cyanobacteria where surface motility powered by type 4 pili (T4P) is common and facilitates phototaxis to seek out favorable light environments. In cyanobacteria, chemotaxis-like systems are known to regulate motility and phototaxis. The characterized phototaxis systems rely on methyl-accepting chemotaxis proteins containing bilin-binding GAF domains capable of directly sensing light, and the mechanism by which they regulate the T4P is largely undefined. In this study we demonstrate that cyanobacteria possess a second, GAF-independent, means of sensing light to regulate motility and provide insight into how a chemotaxis-like system regulates the T4P motors. A combination of genetic, cytological, and protein-protein interaction analyses, along with experiments using the proton ionophore carbonyl cyanide m-chlorophenyl hydrazine, indicate that the Hmp chemotaxis-like system of the model filamentous cyanobacterium is capable of sensing light indirectly, possibly via alterations in proton motive force, and modulates direct interaction between the cyanobacterial taxis protein HmpF, and Hfq, PilT1, and PilT2 to regulate the T4P motors. Given that the Hmp system is widely conserved in cyanobacteria, and the finding from this study that orthologs of HmpF and T4P proteins from the distantly related model unicellular cyanobacterium sp. strain PCC6803 interact in a similar manner to their counterparts, it is likely that this represents a ubiquitous means of regulating motility in response to light in cyanobacteria.
运动性在原核生物中普遍存在，包括进行表面运动的光合蓝细菌，这种运动由 IV 型菌毛（T4P）提供动力，有助于趋光寻找有利的光照环境。在蓝细菌中，已知趋化作用样系统调节运动性和趋光性。已鉴定的趋光系统依赖于含有视黄醛结合 GAF 结构域的甲基受体趋化蛋白，该结构域能够直接感应光，而它们调节 T4P 的机制在很大程度上尚不清楚。在这项研究中，我们证明蓝细菌具有第二种独立于 GAF 的感应光的方法来调节运动性，并深入了解类似趋化作用的系统如何调节 T4P 马达。通过遗传、细胞学和蛋白质-蛋白质相互作用分析的组合，以及使用质子离子载体羰基氰化物 m-氯代苯腙的实验，表明模型丝状蓝细菌中的 Hmp 趋化作用样系统能够间接感应光，可能通过质子动力势的改变，并且调节蓝细菌趋化蛋白 HmpF 与 Hfq、PilT1 和 PilT2 之间的直接相互作用，以调节 T4P 马达。鉴于 Hmp 系统在蓝细菌中广泛保守，并且本研究发现来自远缘的模式单细胞蓝细菌 sp. 菌株 PCC6803 的 HmpF 和 T4P 蛋白的同源物以类似的方式相互作用，因此，这可能代表了一种普遍的调节运动性以响应蓝细菌中光的方式。
