Assembly and function of the archaeal flagellum

Molecular Biology of Archaea, Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Strasse 10, 35043 Marburg, Germany.
Biochemical Society Transactions (Impact Factor: 3.19). 02/2011; 39(1):64-9. DOI: 10.1042/BST0390064
Source: PubMed


Motility is a common behaviour in prokaryotes. Both bacteria and archaea use flagella for swimming motility, but it has been well documented that structures of the flagellum from these two domains of life are completely different, although they contribute to a similar function. Interestingly, information available to date has revealed that structurally archaeal flagella are more similar to bacterial type IV pili rather than to bacterial flagella. With the increasing genome sequence information and advancement in genetic tools for archaea, identification of the components involved in the assembly of the archaeal flagellum is possible. A subset of these components shows similarities to components from type IV pilus-assembly systems. Whereas the molecular players involved in assembly of the archaeal flagellum are being identified, the mechanics and dynamics of the assembly of the archaeal flagellum have yet to be established. Recent computational analysis in our laboratory has identified conserved highly charged loop regions within one of the core proteins of the flagellum, the membrane integral protein FlaJ, and predicted that these are involved in the interaction with the assembly ATPase FlaI. Interestingly, considerable variation was found among the loops of FlaJ from the two major subkingdoms of archaea, the Euryarchaeota and the Crenarchaeota. Understanding the assembly pathway and creating an interaction map of the molecular players in the archaeal flagellum will shed light on the details of the assembly and also the evolutionary relationship to the bacterial type IV pili-assembly systems.

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    • "His 6 -tagged PfFlaI was purified and precipitated using 80 % (w/v) ammonium sulfate and resuspended in a buffer containing 50 mM Tris-HCl pH 8, 150 mM NaCl. SaFlaI and SaFlaXc and its variants were purified as described (Ghosh et al., 2011)(Banerjee et al., 2012). "
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    ABSTRACT: The motor of the membrane-anchored archaeal motility structure, the archaellum, contains FlaX, FlaI, and FlaH. FlaX forms a 30nm ring structure that acts as a scaffold protein and was shown to interact with the bifunctional ATPase FlaI and FlaH. However, the structure and function of FlaH has been enigmatic. Here we present structural and functional analyses of isolated FlaH and archaellum motor subcomplexes. The FlaH crystal structure reveals a RecA/Rad51 family fold with an ATP bound on a conserved and exposed surface, which presumably forms an oligomerization interface. FlaH does not hydrolyze ATP in vitro, but ATP binding to FlaH is essential for its interaction with FlaI and for archaellum assembly. FlaH interacts with the C-terminus of FlaX, which was earlier shown to be essential for FlaX ring formation and to mediate interaction with FlaI. Electron microscopy reveals that FlaH assembles as a second ring inside the FlaX ring in vitro. Collectively these data reveal central structural mechanisms for FlaH interactions in mediating archaellar assembly: FlaH binding within the FlaX ring and nucleotide-regulated FlaH binding to FlaI form the archaellar basal body core.
    Molecular Microbiology 10/2015; DOI:10.1111/mmi.13260 · 4.42 Impact Factor
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    • "PibD, a membrane-bound aspartic acid protease, specifically cleaves the signal sequence of FlaB (Albers et al., 2003; Szabo et al., 2007). FlaI, the dual function ATPase is involved in both archaellum assembly and rotation (Ghosh et al., 2011; Reindl et al., 2013). FlaH (H) is a unknown function RecA family protein. "
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    ABSTRACT: Archaea employ the archaellum, a type IV pilus-like nanomachine, for swimming motility. In the crenarchaeon Sulfolobus acidocaldarius, the archaellum consists of seven proteins: FlaB/X/G/F/H/I/J. FlaF is conserved and essential for archaellum assembly but no FlaF structures exist. Here, we truncated the FlaF N terminus and solved 1.5-Å and 1.65-Å resolution crystal structures of this monotopic membrane protein. Structures revealed an N-terminal α-helix and an eight-strand β-sandwich, immunoglobulin-like fold with striking similarity to S-layer proteins. Crystal structures, X-ray scattering, and mutational analyses suggest dimer assembly is needed for in vivo function. The sole cell envelope component of S. acidocaldarius is a paracrystalline S-layer, and FlaF specifically bound to S-layer protein, suggesting that its interaction domain is located in the pseudoperiplasm with its N-terminal helix in the membrane. From these data, FlaF may act as the previously unknown archaellum stator protein that anchors the rotating archaellum to the archaeal cell envelope. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
    Structure 04/2015; 23(5). DOI:10.1016/j.str.2015.03.001 · 5.62 Impact Factor
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    • "Archaea are known to use the type IV pili-like model to assemble numerous surface structures [2], [3], [25], [26] including type IV-like pili [25], [26], [29]–[32], the bindosome for substrate uptake in Sulfolobus solfataricus [25], [33], [34]),likely the unusual Iho670 fibres of Ignicoccus hospitalis [35], [36] and the best studied example, namely the archaellum [25], [28], [37]–[40]. The name “archaellum” has been proposed to replace the term “archaeal flagellum” [27] since the archaeal structure, while involved in swimming (as well as other functions), is not homologous to the bacterial flagellum and is related instead to type IV pili in structure and likely assembly [28], [41], [42]. "
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    ABSTRACT: Methanococcus maripaludis is an archaeon with two studied surface appendages, archaella and type IV-like pili. Previously, the major structural pilin was identified as MMP1685 and three additional proteins were designated as minor pilins (EpdA, EpdB and EpdC). All of the proteins are likely processed by the pilin-specific prepilin peptidase EppA. Six other genes were identified earlier as likely encoding pilin proteins processed also by EppA. In this study, each of the six genes (mmp0528, mmp0600, mmp0601, mmp0709, mmp0903 and mmp1283) was deleted and the mutants examined by electron microscopy to determine their essentiality for pili formation. While mRNA transcripts of all genes were detected by RT-PCR, only the deletion of mmp1283 led to nonpiliated cells. This strain could be complemented back to a piliated state by supplying a wildtype copy of the mmp1283 gene in trans. This study adds to the complexity of the type IV pili system in M. maripaludis and raises questions about the functions of the remaining five pilin-like genes and whether M. maripaludis under other growth conditions may be able to assemble additional pili-like structures.
    PLoS ONE 12/2013; 8(12):e83961. DOI:10.1371/journal.pone.0083961 · 3.23 Impact Factor
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