Structural insights into the mechanism of archaellar rotational switching

Abstract

Signal transduction via phosphorylated CheY towards the flagellum and the archaellum involves a conserved mechanism of CheY phosphorylation and subsequent conformational changes within CheY. This mechanism is conserved among bacteria and archaea, despite substantial differences in the composition and architecture of archaellum and flagellum, respectively. Phosphorylated CheY has higher affinity towards the bacterial C-ring and its binding leads to conformational changes in the flagellar motor and subsequent rotational switching of the flagellum. In archaea, the adaptor protein CheF resides at the cytoplasmic face of the archaeal C-ring formed by the proteins ArlCDE and interacts with phosphorylated CheY. While the mechanism of CheY binding to the C-ring is well-studied in bacteria, the role of CheF in archaea remains enigmatic and mechanistic insights are absent. Here, we have determined the atomic structures of CheF alone and in complex with activated CheY by X-ray crystallography. CheF forms an elongated dimer with a twisted architecture. We show that CheY binds to the C-terminal tail domain of CheF leading to slight conformational changes within CheF. Our structural, biochemical and genetic analyses reveal the mechanistic basis for CheY binding to CheF and allow us to propose a model for rotational switching of the archaellum.

Putative nucleotide-based second messengers in archaea

“…Whereas the most observed output of bacterial two-component systems is the regulation of transcription, this seems less the case for archaea, where only a small number of two-component systems have a DNA-binding output domain (Galperin et al 2018 , Krell 2018 ). Indeed, the well-studied Che chemosensory pathway is a more sophisticated version of a two-component system and plays an important role in regulating the rotational direction of the archaellum, the archaeal motility structure, in response to external stimuli (Quax et al 2018 , Altegoer et al 2022 ). Reversible phosphorylation of proteins by protein kinases and phosphatases in response to external stimuli can also be used to transduce signals (Esser et al 2016 ).…”

“…This cap can be methylated and can protect mRNA from degradation, thus stabilizing mRNA (Hudeček et al 2020 ). In Bacillus subtilis , Ap 4 A regulates inosine-5′-monophosphate dehydrogenase, thus affecting nucleotide metabolite homoeostasis (Altegoer et al 2022 ). Ap 4 A also binds to other ATP-binding proteins; however, it has been questioned whether it only binds to an ATP analog (Despotović et al 2017 ).…”