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.
"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. "
"Archaea are known to use the type IV pili-like model to assemble numerous surface structures , , ,  including type IV-like pili , , –, the bindosome for substrate uptake in Sulfolobus solfataricus
, , ),likely the unusual Iho670 fibres of Ignicoccus hospitalis
,  and the best studied example, namely the archaellum , , –. The name “archaellum” has been proposed to replace the term “archaeal flagellum”  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 , , . "
[Show abstract][Hide abstract] 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
"In addition, major pseudopilin mutations lead to changes in substrate specificity in Xcp and Hxc, the two T2SS of P. aeruginosa (Durand et al., 2011). Evidence for rotation during or upon assembly of helical fibers comes from archaella, which rotate to promote swimming (Ghosh and Albers, 2011; Herzog and Wirth, 2012 and S.V. Albers, personal communication). While bacterial flagella require proton motive force for rotation, archaella use the energy of ATP hydrolysis and do not seem to require motor proteins other than the assembly machinery itself (Streif et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: Type II secretion systems (T2SSs) share common origins and structure with archaeal flagella (archaella) and pili, bacterial competence systems and type IV pili. All of these systems use a conserved ATP-powered machinery to assemble helical fibers that are anchored in the plasma membrane. The T2SSs assemble pseudopili, periplasmic filaments that promote extracellular secretion of folded periplasmic proteins. Comparative analysis of T2SSs and related fiber assembly nanomachines might provide important clues on their functional specificities and dynamics. This review focuses on recent developments in the study of pseudopilus structure and biogenesis, and discusses mechanistic models of pseudopilus function in protein secretion.
Research in Microbiology 03/2013; 164(6). DOI:10.1016/j.resmic.2013.03.013 · 2.71 Impact Factor
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