Electron cryo-microscopy reveals the structure of the archaeal thread filament

Abstract

Pili are filamentous surface extensions that play roles in bacterial and archaeal cellular processes such as adhesion, biofilm formation, motility, cell-cell communication, DNA uptake and horizontal gene transfer. The model archaeaon Sulfolobus acidocaldarius assembles three filaments of the type-IV pilus superfamily (archaella, archaeal adhesion pili and UV-inducible pili), as well as a so-far uncharacterised fourth filament, named “thread”. Here, we report on the cryo-EM structure of the archaeal thread. The filament is highly glycosylated and consists of subunits of the protein Saci_0406, arranged in a head-to-tail manner. Saci_0406 displays structural similarity, but low sequence homology, to bacterial type-I pilins. Thread subunits are interconnected via donor strand complementation, a feature reminiscent of bacterial chaperone-usher pili. However, despite these similarities in overall architecture, archaeal threads appear to have evolved independently and are likely assembled by a distinct mechanism.

Stay or Go: Sulfolobales Biofilm Dispersal Is Dependent on a Bifunctional VapB Antitoxin

“…Furthermore, Δ vapC14 toxin mutant 4-day planktonic cultures were devoid of most surface appendages, supporting the VapC14 toxin’s regulation of Aap pili and archaella in planktonic cells. Thin structures referred to as “threads,” which are structurally similar to type I pili ( 42 ), were unaffected by the VapBC14 TA system as they were seen in every strain at similar levels. However, the Δ vapBC14 double mutant biofilm was hyperpiliated with Ups pili and hyperarchaellated in planktonic culture, which may be stress responses to the loss of other surface appendage structures.…”

Tat-fimbriae (“tafi”) – novel type of haloarchaeal surface structures

“…The development of the unique method of cryo-electron microscopy and new bioinformatic servers such as AlphaFold and DALI have remarkably improved the possibilities of studying the structure and mechanisms of various biological supramolecular complexes. Recently, two teams of researchers reported on the atomic structures of two previously uncharacterized archaeal surface filaments: the bundling pili of Pyrobaculum calidifontis (Wang et al ., 2022) and the thread filament of Sulfolobus acidocaldarius (Gaines et al ., 2022) determined using the cryo-electron microscopy and AlphaFold. Both filamentous structures show a striking resemblance to type I bacterial adhesive pili.…”

Mechanism of bacterial predation via ixotrophy

“…Finally, the cells were harvested (7,000 g, room temperature, 20 min), and the cell pellet was thoroughly resuspended in 48 mL grappling hook shearing buffer (150 mM NaCl, 20 mM HEPES, pH7.5, 1x cOmplete EDTA-free protease inhibitor tablet) until all clumps were dissolved. The grappling hook shearing protocol was adapted from Gaines, M. C. et al (Gaines et al , 2022). Briefly, the vial with the cell suspension was connected to a peristaltic pump and, under gentle stirring using a magnetic stirrer, continuously passed through two needles (0.8 mm x 40 mm, 4 °C, 3 h, Microlance 3, VVR and 0.5 mm x 16 mm, 4 °C, overnight, Microlance 3, VVR) at 25 rpm.…”