Atypical chemoreceptor arrays accommodate high membrane curvature

Abstract

The prokaryotic chemotaxis system is arguably the best-understood signaling pathway in biology, but most insights have been obtained from only a few model organisms. In all previously described species, chemoreceptors organize with the histidine kinase (CheA) and coupling protein (CheW) into a hexagonal (P6 symmetry) extended array that is considered universal among archaea and bacteria. Here, for the first time, we apply cryo-electron tomography to whole Treponema denticola (Td) cells to investigate the structure of a spirochete (F2) chemotaxis system. The Td chemoreceptor arrays assume a truly unusual arrangement of the supra-molecular protein assembly that has likely evolved to accommodate the high membrane curvature present in spirochetes. A two-fold (P2) symmetry of the chemotaxis apparatus in Td emerges from a strict linear organization of the kinase CheA, which generates arrays that run parallel to the cell axis. The arrays have several additional atypical features, such as an extended dimerization domain of CheA and a variant CheW-CheR-like fusion protein that is critical for maintaining an ordered, functional chemosensory apparatus in an extremely curved cell. Furthermore, the previously characterized Td oxygen sensor ODP influences array integrity and its loss substantially orders CheA. These results demonstrate the importance of examining chemotaxis structures of non-model organisms in vivo and suggest a greater diversity of this signaling system than previously thought.

UVC inactivation of pathogenic samples suitable for cryoEM analysis

“…We show that while the bacterial pathogen V. cholerae is completely inactivated by UVC, the cell’s ultrastructure is indistinguishable from untreated samples. More specifically, using the F6 chemotaxis array as an example, we show that the STA results (reaching resolutions between 2-3 nm) are similar to the published literature for complexes of similar size and in cells with similar thicknesses (Berger et al, 2021; Wolff et al, 2020; Yang et al, 2019; Muok et al, 2020).…”

A new class of protein sensor links spirochete pleomorphism, persistence, and chemotaxis

“…Previous findings show that this additional domain, called CheR like , is widespread among the spirochaetes (Fig. 1B) 29,30 . It is a distant homolog of the chemotaxis protein CheR, which methylates receptors using the methyl-donor S-adenosyl methionine (SAM) as part of an adaptation response 31,32 .…”

“…Furthermore, it has been recently shown that Td cells can actively move from oral cavities to brain tissues where they induce structures associated with Alzheimer’s disease in mice 28 , although the role of chemotaxis in this process is unknown. Recent research with Td has revealed that the structure of the chemotaxis system in spirochetes differs from canonical systems in several regards 29 . Their chemotaxis arrays have unique linear symmetry and contain a novel CheW variant that possesses an additional C-terminal domain.…”

“…In prokaryotes specifically, SAM is essential for synthesis of some amino acids and may be important for microbiome interactions 34,35 . CheR like can bind SAM but does not possess the conserved residues for enzyme catalysis or receptor binding 29,31,36 . Thus, the exact cellular role of this domain remained unclear.…”

Alternative architecture of theE. colichemosensory array

“…The question thus emerges: what are the molecular origins of the p2 symmetric architecture seen in this study? While to the best of our knowledge a p2 symmetric architecture has not yet been reported for the E. coli chemosensory array, a recent publication by Muok et al describes an unusual chemosensory array organisation in the spirochete Treponema denticola [39]. Similar to the p2 lattice described in this study, the atypical T. denticola array exhibits a linear CheA arrangement, including rings involving interactions between a classical CheW and a spirochete-specific CheW variant that are analogous to the (A.P5/W/W)2 rings seen in our model.…”