The crystal structure of the soluble domain of Sulfolobus acidocaldarius FlaF (residues 35-164)

Experimental Data Snapshot

  • Resolution: 1.65 Å
  • R-Value Free: 0.200 
  • R-Value Work: 0.173 
  • R-Value Observed: 0.174 

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FlaF Is a beta-Sandwich Protein that Anchors the Archaellum in the Archaeal Cell Envelope by Binding the S-Layer Protein.

Banerjee, A.Tsai, C.L.Chaudhury, P.Tripp, P.Arvai, A.S.Ishida, J.P.Tainer, J.A.Albers, S.V.

(2015) Structure 23: 863-872

  • DOI: https://doi.org/10.1016/j.str.2015.03.001
  • Primary Citation of Related Structures:  
    4P94, 4ZBH

  • PubMed 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.

  • Organizational Affiliation

    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.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Conserved flagellar protein F
A, B
146Sulfolobus acidocaldarius DSM 639Mutation(s): 0 
Gene Names: Saci_1175
Find proteins for Q4J9K8 (Sulfolobus acidocaldarius (strain ATCC 33909 / DSM 639 / JCM 8929 / NBRC 15157 / NCIMB 11770))
Explore Q4J9K8 
Go to UniProtKB:  Q4J9K8
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ4J9K8
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on NA

Download Ideal Coordinates CCD File 
Experimental Data & Validation

Experimental Data

  • Resolution: 1.65 Å
  • R-Value Free: 0.200 
  • R-Value Work: 0.173 
  • R-Value Observed: 0.174 
  • Space Group: I 2 3
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 127.257α = 90
b = 127.257β = 90
c = 127.257γ = 90
Software Package:
Software NamePurpose
SCALAdata scaling
PDB_EXTRACTdata extraction

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2015-04-22
    Type: Initial release
  • Version 1.1: 2015-05-27
    Changes: Database references
  • Version 1.2: 2017-11-22
    Changes: Database references, Derived calculations, Other, Refinement description, Source and taxonomy
  • Version 1.3: 2023-09-27
    Changes: Data collection, Database references, Refinement description