Summary
Chemotaxis allows cells to sense and respond to their environment. In bacteria, stimuli are detected by arrays of chemoreceptors that relay the signal to a two-component regulatory system. These arrays take the form of highly stereotyped super-lattices comprising hexagonally packed trimers-of-receptor-dimers networked by rings of histidine kinase and coupling proteins. This structure is conserved across chemotactic bacteria, and between membrane-bound and cytoplasmic arrays, and gives rise to the highly cooperative, dynamic nature of the signaling system. The chemotaxis system, absent in eukaryotes, is also found in archaea, where its structural details remain uncharacterized. Here we provide evidence that the chemotaxis machinery was not present in the last archaeal common ancestor, but rather was introduced in one of the waves of lateral gene transfer that occurred after the branching of Eukaryota but before the diversification of Euryarchaeota. Unlike in Bacteria, the chemotaxis system then evolved largely vertically in Archaea, with very few subsequent successful lateral gene transfer events. By electron cryotomography (ECT), we find that the structure of both membrane-bound and cytoplasmic chemoreceptor arrays is conserved between Bacteria and Archaea, suggesting the fundamental importance of this signaling architecture across diverse prokaryotic lifestyles.
Data information: s, S-layer; m, membrane; c, conical structure; a, archaella; r, ring. Scale bars, 100 nm; scale bar in (A) applies to (1-3); scale bar in (B) applies to (B-E).
EMBO reportsª 2017 The Authors
EMBO reportsStructure of an archaellar motor and cone Ariane Briegel et al EV1 Figure EV2. Double-cone structure observed in Thermococcus kodakaraensis.A tomographic slice through a side view shows two associated conical structures (c1 and c2), both associated with archaella (a). s, S-layer; m, membrane. Scale bar, 100 nm. A, B Tomographic slices through two cells, highlighting the association between the cone and the archaella. C, D 3D segmentations of the cells in (A) and (B), respectively, with cones in blue and archaella in red, embedded in tomographic slices. E Tomographic slices of individual archaella show the varying orientations of archaella with respect to the cell envelope, as well as apparent connections to the cone.Data information: Scale bars, 100 nm in (A) and (B), 50 nm in (E) (applies to all panels in E); segmentations not to scale. Figure EV4. Individual particles from the subtomogram average show heterogeneity in the L3 density and angle of cone density.
EMBO reportsª 2017 The Authors EMBO reports Structure of an archaellar motor and cone Ariane Briegel et al EV3The L3 density appears as either two dots of similar (first two panels) or different intensity (third panel), a single dot (fourth panel), or a dot and an extended line (fifth panel). m, membrane; c, conical structure. Scale bar, 10 nm (applies to all panels).ª 2017 The Authors EMBO reportsAriane Briegel et al Structure of an archaellar motor and cone EMBO reports EV4
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