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The archaellum: how Archaea swim.

Albers SV, Jarrell KF - Front Microbiol (2015)

Bottom Line: Recent studies on archaeal motility have shown that the archaeal motility structure is unique in several aspects.Although it fulfills the same swimming function as the bacterial flagellum, it is evolutionarily and structurally related to the type IV pilus.This was the basis for the recent proposal to term the archaeal motility structure the "archaellum." This review illustrates the key findings that led to the realization that the archaellum was a novel motility structure and presents the current knowledge about the structural composition, mechanism of assembly and regulation, and the posttranslational modifications of archaella.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology of Archaea, Institute of Biology II-Microbiology, University of Freiburg , Freiburg, Germany ; Molecular Biology of Archaea, Max Planck Institute for Terrestrial Microbiology , Marburg, Germany.

ABSTRACT
Recent studies on archaeal motility have shown that the archaeal motility structure is unique in several aspects. Although it fulfills the same swimming function as the bacterial flagellum, it is evolutionarily and structurally related to the type IV pilus. This was the basis for the recent proposal to term the archaeal motility structure the "archaellum." This review illustrates the key findings that led to the realization that the archaellum was a novel motility structure and presents the current knowledge about the structural composition, mechanism of assembly and regulation, and the posttranslational modifications of archaella.

No MeSH data available.


Related in: MedlinePlus

Overview of the factors that influence the expression of the S. acidocaldarius archaellum operon. The one component membrane factors ArnR/R1, as well as the biofilm regulator AbfR1, are positive regulators of the flaB promoter. The two kinases ArnC and ArnD (Saci_1193 and Saci_1694, respectively), here depicted as ePK (eukaryotic like protein kinase) phosphorylate ArnA and ArnB which leads to repression of flaB expression. Deletion mutants of the phosphatase PP2A have a hypermotile phenotype, however, the specific target of the phosphatase is not known.
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Figure 4: Overview of the factors that influence the expression of the S. acidocaldarius archaellum operon. The one component membrane factors ArnR/R1, as well as the biofilm regulator AbfR1, are positive regulators of the flaB promoter. The two kinases ArnC and ArnD (Saci_1193 and Saci_1694, respectively), here depicted as ePK (eukaryotic like protein kinase) phosphorylate ArnA and ArnB which leads to repression of flaB expression. Deletion mutants of the phosphatase PP2A have a hypermotile phenotype, however, the specific target of the phosphatase is not known.

Mentions: However, it is in the crenarchaea that most of the information concerning regulation of archaella is known. It was demonstrated in S. solfataricus that starvation induced the expression of the archaellum operon (Szabo et al., 2007b). In S. acidocaldarius, a number of components of the archaellum regulatory network (termed Arn proteins) were identified. ArnA, containing a fork head associated (FHA) domain and a zinc finger domain, was first shown in S. tokodaii (Wang et al., 2010) to be phosphorylated by kinase ST1565. A screen with S. tokodaii promoters identified the flaX promoter as a target, which was only bound when ArnA was in the phosphorylated state (Duan and He, 2011). ArnA is co-transcribed in an operon with ArnB, which contains a van Willebrand domain. These two proteins were demonstrated to strongly interact with each other both in vitro and in vivo in S. acidocaldarius (Reimann et al., 2012). As FHA domain containing proteins are known to bind to phosphorylated tyrosines, it is proposed that the ArnA and ArnB interaction relies on protein phosphorylation. Deletion of ArnA, ArnB or the zinc finger of ArnA led to the overexpression of archaella in S. acidocaldarius even without starvation conditions, indicating that both proteins act as repressors of the archaellum operon (see Figure 4; Reimann et al., 2012). In the fla operons of Sulfolobales, three other conserved proteins were identified, Saci_1180 (ArnR), Saci_1171 (ArnR1) and Saci_1179. Saci_1179 is a small membrane protein; deletion of the corresponding gene did not lead to any deregulation of archaella in S. acidocaldarius (Lassak et al., 2013). On the contrary, deletion of Saci_1180 completely inhibited expression of FlaB (Lassak et al., 2013). Saci_1180 is a membrane bound one-component regulator, termed ArnR, with an N-terminal helix trun helix (HTH) domain and two C-terminal transmembrane domains (Figure 4). In between these two domains a possible sensing domain is present which is believed to transmit a signal to the HTH domain. Interestingly, only in S. acidocaldarius, a gene duplication has occurred as downstream of flaJ, an arnR paralog is present, termed arnR1 (see Figure 4). The HTH domains of ArnR and ArnR1 are nearly identical, whereas their sensing domains are quite different. Deletion of ArnR1 had a much less severe effect on flaB expression, indicating that it might be involved in fine tuning the expression of flaB. The archaellum operon in S. acidocaldarius has two transcriptional units of which one is flaB and the other locus is flaX-J (see Figure 4; Lassak et al., 2012b). Promoter fusion assays showed that ArnR and ArnR1 regulate the flaB promoter but not the flaX-J promoter. Moreover two inverted repeats, which are essential for the transcription of flaB, were identified in the promoter region of flaB (Lassak et al., 2012b).


The archaellum: how Archaea swim.

Albers SV, Jarrell KF - Front Microbiol (2015)

Overview of the factors that influence the expression of the S. acidocaldarius archaellum operon. The one component membrane factors ArnR/R1, as well as the biofilm regulator AbfR1, are positive regulators of the flaB promoter. The two kinases ArnC and ArnD (Saci_1193 and Saci_1694, respectively), here depicted as ePK (eukaryotic like protein kinase) phosphorylate ArnA and ArnB which leads to repression of flaB expression. Deletion mutants of the phosphatase PP2A have a hypermotile phenotype, however, the specific target of the phosphatase is not known.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4307647&req=5

Figure 4: Overview of the factors that influence the expression of the S. acidocaldarius archaellum operon. The one component membrane factors ArnR/R1, as well as the biofilm regulator AbfR1, are positive regulators of the flaB promoter. The two kinases ArnC and ArnD (Saci_1193 and Saci_1694, respectively), here depicted as ePK (eukaryotic like protein kinase) phosphorylate ArnA and ArnB which leads to repression of flaB expression. Deletion mutants of the phosphatase PP2A have a hypermotile phenotype, however, the specific target of the phosphatase is not known.
Mentions: However, it is in the crenarchaea that most of the information concerning regulation of archaella is known. It was demonstrated in S. solfataricus that starvation induced the expression of the archaellum operon (Szabo et al., 2007b). In S. acidocaldarius, a number of components of the archaellum regulatory network (termed Arn proteins) were identified. ArnA, containing a fork head associated (FHA) domain and a zinc finger domain, was first shown in S. tokodaii (Wang et al., 2010) to be phosphorylated by kinase ST1565. A screen with S. tokodaii promoters identified the flaX promoter as a target, which was only bound when ArnA was in the phosphorylated state (Duan and He, 2011). ArnA is co-transcribed in an operon with ArnB, which contains a van Willebrand domain. These two proteins were demonstrated to strongly interact with each other both in vitro and in vivo in S. acidocaldarius (Reimann et al., 2012). As FHA domain containing proteins are known to bind to phosphorylated tyrosines, it is proposed that the ArnA and ArnB interaction relies on protein phosphorylation. Deletion of ArnA, ArnB or the zinc finger of ArnA led to the overexpression of archaella in S. acidocaldarius even without starvation conditions, indicating that both proteins act as repressors of the archaellum operon (see Figure 4; Reimann et al., 2012). In the fla operons of Sulfolobales, three other conserved proteins were identified, Saci_1180 (ArnR), Saci_1171 (ArnR1) and Saci_1179. Saci_1179 is a small membrane protein; deletion of the corresponding gene did not lead to any deregulation of archaella in S. acidocaldarius (Lassak et al., 2013). On the contrary, deletion of Saci_1180 completely inhibited expression of FlaB (Lassak et al., 2013). Saci_1180 is a membrane bound one-component regulator, termed ArnR, with an N-terminal helix trun helix (HTH) domain and two C-terminal transmembrane domains (Figure 4). In between these two domains a possible sensing domain is present which is believed to transmit a signal to the HTH domain. Interestingly, only in S. acidocaldarius, a gene duplication has occurred as downstream of flaJ, an arnR paralog is present, termed arnR1 (see Figure 4). The HTH domains of ArnR and ArnR1 are nearly identical, whereas their sensing domains are quite different. Deletion of ArnR1 had a much less severe effect on flaB expression, indicating that it might be involved in fine tuning the expression of flaB. The archaellum operon in S. acidocaldarius has two transcriptional units of which one is flaB and the other locus is flaX-J (see Figure 4; Lassak et al., 2012b). Promoter fusion assays showed that ArnR and ArnR1 regulate the flaB promoter but not the flaX-J promoter. Moreover two inverted repeats, which are essential for the transcription of flaB, were identified in the promoter region of flaB (Lassak et al., 2012b).

Bottom Line: Recent studies on archaeal motility have shown that the archaeal motility structure is unique in several aspects.Although it fulfills the same swimming function as the bacterial flagellum, it is evolutionarily and structurally related to the type IV pilus.This was the basis for the recent proposal to term the archaeal motility structure the "archaellum." This review illustrates the key findings that led to the realization that the archaellum was a novel motility structure and presents the current knowledge about the structural composition, mechanism of assembly and regulation, and the posttranslational modifications of archaella.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology of Archaea, Institute of Biology II-Microbiology, University of Freiburg , Freiburg, Germany ; Molecular Biology of Archaea, Max Planck Institute for Terrestrial Microbiology , Marburg, Germany.

ABSTRACT
Recent studies on archaeal motility have shown that the archaeal motility structure is unique in several aspects. Although it fulfills the same swimming function as the bacterial flagellum, it is evolutionarily and structurally related to the type IV pilus. This was the basis for the recent proposal to term the archaeal motility structure the "archaellum." This review illustrates the key findings that led to the realization that the archaellum was a novel motility structure and presents the current knowledge about the structural composition, mechanism of assembly and regulation, and the posttranslational modifications of archaella.

No MeSH data available.


Related in: MedlinePlus