Structure of bacterial cytoplasmic chemoreceptor arrays and implications for chemotactic signaling.
Structure of bacterial cytoplasmic chemoreceptor arrays and implications for chemotactic signaling.
复制标题
细菌细胞质化学感受器阵列的结构及其对趋化信号传导的影响。
DOI：
10.7554/elife.02151
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发表时间：
2014-03-25
期刊：
影响因子：
7.7
通讯作者：
Jensen GJ
中科院分区：
文献类型：
--
作者：
Briegel A;Ladinsky MS;Oikonomou C;Jones CW;Harris MJ;Fowler DJ;Chang YW;Thompson LK;Armitage JP;Jensen GJ
大多数移动细菌通过跨膜化学受体阵列感知环境并对环境做出反应，该阵列的结构和功能已经被很好地研究，但许多物种的细胞质中也含有额外的化学受体簇。尽管细胞质簇对于某些生物体的正常趋化是必不可少的，但它的结构和功能仍不清楚。在这里，我们使用电子冷冻断层扫描技术对球形红杆菌和霍乱弧菌的细胞质化学感受器簇进行成像。我们发现，就像跨膜阵列一样，细胞质簇包含以12纳米六角阵列组织的受体二聚体的三聚体。然而，与跨膜阵列不同的是，细胞质簇包括两个CHEA/CHEW基板，中间夹着两个相对的受体阵列。我们进一步证明，在分子拥挤剂存在的情况下，正常跨膜大肠杆菌化学受体的细胞质片段形成类似的夹心结构。总而言之，这些结果表明，12 nm的六角形结构是基本重要的，夹层和拥挤可以取代膜的稳定作用。DOI：http://dx.doi.org/10.7554/eLife.02151.001许多细菌通过旋转称为鞭毛的微小毛发状结构在水中游泳。在大肠杆菌中，如果细菌表面的所有鞭毛都以逆时针的方式旋转，那么它就会朝着特定的方向游泳，但如果鞭毛都沿顺时针旋转，那么细菌就会停止游泳，开始翻滚。细菌使用游泳和翻滚相结合的方式来接近或远离某些化学物质。例如，细菌之所以能够向营养来源移动，是因为它不断评估自己的环境，当它意识到营养浓度正在增加时，它会向前游更长的时间。如果它感觉到营养浓度在下降，它就会翻滚，努力朝着不同的方向移动。许多细菌，如大肠杆菌，依靠细胞膜上称为化学感受器的蛋白质来感知特定的化学物质，然后发送信号告诉鞭毛如何旋转。这些跨膜受体及其在趋化作用中的作用--即向环境中的特定化学物质移动或远离环境中的特定化学物质--已被广泛研究。然而，其他细菌在细菌细胞内的细胞质中也有化学感受器，对此知之甚少。现在，Briegel等人。研究了两种无关细菌球状杆菌和霍乱弧菌的细胞质化学受体，发现细胞质化学受体以六角形排列，类似于跨膜化学受体的排列方式。然而，细胞质化学感受器以双层夹心状结构排列，而跨膜化学感受器仅排列在一层。下一步是了解化学结合是如何导致这些阵列向电机发送信号的。对这一信号系统的完全了解可能最终会让科学家们重新设计它，将细菌吸引到具有医学或环境意义的目标，如癌细胞或受污染的土壤。DOI：http://dx.doi.org/10.7554/eLife.02151.002
Most motile bacteria sense and respond to their environment through a transmembrane chemoreceptor array whose structure and function have been well-studied, but many species also contain an additional cluster of chemoreceptors in their cytoplasm. Although the cytoplasmic cluster is essential for normal chemotaxis in some organisms, its structure and function remain unknown. Here we use electron cryotomography to image the cytoplasmic chemoreceptor cluster in Rhodobacter sphaeroides and Vibrio cholerae. We show that just like transmembrane arrays, cytoplasmic clusters contain trimers-of-receptor-dimers organized in 12-nm hexagonal arrays. In contrast to transmembrane arrays, however, cytoplasmic clusters comprise two CheA/CheW baseplates sandwiching two opposed receptor arrays. We further show that cytoplasmic fragments of normally transmembrane E. coli chemoreceptors form similar sandwiched structures in the presence of molecular crowding agents. Together these results suggest that the 12-nm hexagonal architecture is fundamentally important and that sandwiching and crowding can replace the stabilizing effect of the membrane. DOI: http://dx.doi.org/10.7554/eLife.02151.001 Many bacteria swim through water by rotating tiny hair-like structures called flagella. In E. coli, if all the flagella on the surface of a bacterium rotate in a counterclockwise fashion, then it will swim in a particular direction, but if the flagella all rotate in an clockwise fashion, then the bacterium will stop swimming and start to tumble. Bacteria use a combination of swimming and tumbling in order to move towards or away from certain chemicals. For example, a bacterium is able to move towards a source of nutrients because it is constantly evaluating its environment and will swim forward for longer periods of time when it recognizes the concentration of the nutrient is increasing. And if it senses that the nutrient concentration is decreasing, it will tumble in an effort to move in a different direction. Many bacteria, such as E. coli, rely on proteins in their cell membrane called chemoreceptors to sense specific chemicals and then send signals that tell the flagella how to rotate. These transmembrane receptors and their role in chemotaxis—that is, movement towards or away from specific chemicals in the environment—have been widely studied. However, other bacteria also have chemoreceptors in the cytoplasm inside the bacterial cell, and much less is known about these. Now, Briegel et al. have examined the cytoplasmic chemoreceptors of two unrelated bacteria, R. sphaeroides and V. cholera, and found that the cytoplasmic chemoreceptors arrange themselves in hexagonal arrays, similar to the way that transmembrane chemoreceptors are arranged. However, the cytoplasmic chemoreceptors arrange themselves in a two-layer sandwich-like structure, whereas the transmembrane chemoreceptors are arranged in just one layer. The next step is to understand how chemical binding causes these arrays to send their signals to the motor. A complete understanding of this signaling system may ultimately allow scientists to re-engineer it to draw bacteria to targets of medical or environmental interest, such as cancer cells or contaminated soils. DOI: http://dx.doi.org/10.7554/eLife.02151.002