July 7, 2019  |  

Structure of a 1.5-MDa adhesin that binds its Antarctic bacterium to diatoms and ice.

Authors: Guo, Shuaiqi and Stevens, Corey A and Vance, Tyler D R and Olijve, Luuk L C and Graham, Laurie A and Campbell, Robert L and Yazdi, Saeed R and Escobedo, Carlos and Bar-Dolev, Maya and Yashunsky, Victor and Braslavsky, Ido and Langelaan, David N and Smith, Steven P and Allingham, John S and Voets, Ilja K and Davies, Peter L

Bacterial adhesins are modular cell-surface proteins that mediate adherence to other cells, surfaces, and ligands. The Antarctic bacterium Marinomonas primoryensis uses a 1.5-MDa adhesin comprising over 130 domains to position it on ice at the top of the water column for better access to oxygen and nutrients. We have reconstructed this 0.6-µm-long adhesin using a "dissect and build" structural biology approach and have established complementary roles for its five distinct regions. Domains in region I (RI) tether the adhesin to the type I secretion machinery in the periplasm of the bacterium and pass it through the outer membrane. RII comprises ~120 identical immunoglobulin-like ß-sandwich domains that rigidify on binding Ca(2+) to project the adhesion regions RIII and RIV into the medium. RIII contains ligand-binding domains that join diatoms and bacteria together in a mixed-species community on the underside of sea ice where incident light is maximal. RIV is the ice-binding domain, and the terminal RV domain contains several "repeats-in-toxin" motifs and a noncleavable signal sequence that target proteins for export via the type I secretion system. Similar structural architecture is present in the adhesins of many pathogenic bacteria and provides a guide to finding and blocking binding domains to weaken infectivity.

Journal: Science advances
DOI: 10.1126/sciadv.1701440
Year: 2017

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