title: FlaF Is a β-Sandwich Protein that Anchors the Archaellum in the Archaeal Cell Envelope by Binding the S-Layer Protein.
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.
authors: Molecular Biology of Archaea, Max Planck Institute for terrestrial Microbiology, Karl-von-Frisch-Strasse 10, 35043 Marburg, Germany.
authors: Ankan
authors: A
authors: Banerjee
authors: Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
authors: Chi-Lin
authors: CL
authors: Tsai
authors: Molecular Biology of Archaea, Max Planck Institute for terrestrial Microbiology, Karl-von-Frisch-Strasse 10, 35043 Marburg, Germany; Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Schaenzlestrasse 1, 79211 Freiburg, Germany.
authors: Paushali
authors: P
authors: Chaudhury
authors: Molecular Biology of Archaea, Max Planck Institute for terrestrial Microbiology, Karl-von-Frisch-Strasse 10, 35043 Marburg, Germany; Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Schaenzlestrasse 1, 79211 Freiburg, Germany.
authors: Patrick
authors: P
authors: Tripp
authors: Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors: Andrew S
authors: AS
authors: Arvai
authors: Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
authors: Justin P
authors: JP
authors: Ishida
authors: Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA; Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Electronic address: jatainer@lbl.gov.
authors: John A
authors: JA
authors: Tainer
authors: Molecular Biology of Archaea, Max Planck Institute for terrestrial Microbiology, Karl-von-Frisch-Strasse 10, 35043 Marburg, Germany; Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Schaenzlestrasse 1, 79211 Freiburg, Germany. Electronic address: sonja.albers@biologie.uni-freiburg.de.
authors: Sonja-Verena
authors: SV
authors: Albers
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D017433:Protein Structure, Secondary; D016945:Sulfolobus acidocaldarius / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins