FlaF Is a β-Sandwich Protein that Anchors the Archaellum in the Archaeal Cell Envelope by Binding the S-Layer Protein
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.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 1392695
- Alternate ID(s):
- OSTI ID: 1208647
- Journal Information:
- Structure, Journal Name: Structure Vol. 23 Journal Issue: 5; ISSN 0969-2126
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
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