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| Title | CryoEM structure of a post-assembly MS-ring reveals plasticity in stoichiometry and conformation. |
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| Journal, issue, pages | PLoS One, Vol. 18, Issue 5, Page e0285343, Year 2023 |
| Publish date | May 19, 2023 |
 Authors | Prashant K Singh / Gary Cecchini / Terunaga Nakagawa / T M Iverson /  |
| PubMed Abstract | The flagellar motor supports bacterial chemotaxis, a process that allows bacteria to move in response to their environment. A central feature of this motor is the MS-ring, which is composed entirely ...The flagellar motor supports bacterial chemotaxis, a process that allows bacteria to move in response to their environment. A central feature of this motor is the MS-ring, which is composed entirely of repeats of the FliF subunit. This MS-ring is critical for the assembly and stability of the flagellar switch and the entire flagellum. Despite multiple independent cryoEM structures of the MS-ring, there remains a debate about the stoichiometry and organization of the ring-building motifs (RBMs). Here, we report the cryoEM structure of a Salmonella MS-ring that was purified from the assembled flagellar switch complex (MSC-ring). We term this the 'post-assembly' state. Using 2D class averages, we show that under these conditions, the post-assembly MS-ring can contain 32, 33, or 34 FliF subunits, with 33 being the most common. RBM3 has a single location with C32, C33, or C34 symmetry. RBM2 is found in two locations with RBM2inner having C21 or C22 symmetry and an RBM2outer-RBM1 having C11 symmetry. Comparison to previously reported structures identifies several differences. Most strikingly, we find that the membrane domain forms 11 regions of discrete density at the base of the structure rather than a contiguous ring, although density could not be unambiguously interpreted. We further find density in some previously unresolved areas, and we assigned amino acids to those regions. Finally, we find differences in interdomain angles in RBM3 that affect the diameter of the ring. Together, these investigations support a model of the flagellum with structural plasticity, which may be important for flagellar assembly and function. |
 External links | PLoS One / PubMed:37205674 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 2.9 - 4.1 Å |
| Structure data | EMDB-29424, PDB-8fte: EMDB-29425: CryoEM map of 33-mer RBM3 of the Salmonella MS-ring  EMDB-29427: CryoEM map of 32-mer RBM3 of the Salmonella MS-ring  EMDB-29429: CryoEM map of 34-mer RBM3 of the Salmonella MS-ring  EMDB-29437: CryoEM map of 21-mer RBM2 of the Salmonella MS-ring  EMDB-29441: C11 symmetry applied MS-ring |
| Source |
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 Keywords | MOTOR PROTEIN / flagellar / 22-fold / ring-building motif / MS-ring / FliF / 33-fold |
salmonella enterica subsp. enterica serovar typhimurium (bacteria)