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| Title | Analysis of a flagellar filament cap mutant reveals that HtrA serine protease degrades unfolded flagellin protein in the periplasm of Borrelia burgdorferi. |
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| Journal, issue, pages | Mol Microbiol, Vol. 111, Issue 6, Page 1652-1670, Year 2019 |
| Publish date | Apr 26, 2019 |
 Authors | Kai Zhang / Zhuan Qin / Yunjie Chang / Jun Liu / Michael G Malkowski / Saimtun Shipa / Li Li / Weigang Qiu / Jing-Ren Zhang / Chunhao Li /   |
| PubMed Abstract | Unlike external flagellated bacteria, spirochetes have periplasmic flagella (PF). Very little is known about how PF are assembled within the periplasm of spirochaetal cells. Herein, we report that ...Unlike external flagellated bacteria, spirochetes have periplasmic flagella (PF). Very little is known about how PF are assembled within the periplasm of spirochaetal cells. Herein, we report that FliD (BB0149), a flagellar cap protein (also named hook-associated protein 2), controls flagellin stability and flagellar filament assembly in the Lyme disease spirochete Borrelia burgdorferi. Deletion of fliD leads to non-motile mutant cells that are unable to assemble flagellar filaments and pentagon-shaped caps (10 nm in diameter, 12 nm in length). Interestingly, FlaB, a major flagellin protein of B. burgdorferi, is degraded in the fliD mutant but not in other flagella-deficient mutants (i.e., in the hook, rod, or MS-ring). Biochemical and genetic studies reveal that HtrA, a serine protease of B. burgdorferi, controls FlaB turnover. Specifically, HtrA degrades unfolded but not polymerized FlaB, and deletion of htrA increases the level of FlaB in the fliD mutant. Collectively, we propose that the flagellar cap protein FliD promotes flagellin polymerization and filament growth in the periplasm. Deletion of fliD abolishes this process, which leads to leakage of unfolded FlaB proteins into the periplasm where they are degraded by HtrA, a protease that prevents accumulation of toxic products in the periplasm. |
 External links | Mol Microbiol / PubMed:30883947 / PubMed Central |
| Methods | EM (subtomogram averaging) |
| Resolution | 32.0 Å |
| Structure data |  EMDB-0525: |
| Source |
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Borreliella burgdorferi B31 (bacteria)