Journal: Proc Natl Acad Sci U S A / Year: 2020 Title: The MscS-like channel YnaI has a gating mechanism based on flexible pore helices. Authors: Vanessa Judith Flegler / Akiko Rasmussen / Shanlin Rao / Na Wu / Renato Zenobi / Mark S P Sansom / Rainer Hedrich / Tim Rasmussen / Bettina Böttcher / Abstract: The mechanosensitive channel of small conductance (MscS) is the prototype of an evolutionarily diversified large family that fine-tunes osmoregulation but is likely to fulfill additional functions. ...The mechanosensitive channel of small conductance (MscS) is the prototype of an evolutionarily diversified large family that fine-tunes osmoregulation but is likely to fulfill additional functions. has six osmoprotective paralogs with different numbers of transmembrane helices. These helices are important for gating and sensing in MscS but the role of the additional helices in the paralogs is not understood. The medium-sized channel YnaI was extracted and delivered in native nanodiscs in closed-like and open-like conformations using the copolymer diisobutylene/maleic acid (DIBMA) for structural studies. Here we show by electron cryomicroscopy that YnaI has an extended sensor paddle that during gating relocates relative to the pore concomitant with bending of a GGxGG motif in the pore helices. YnaI is the only one of the six paralogs that has this GGxGG motif allowing the sensor paddle to move outward. Access to the pore is through a vestibule on the cytosolic side that is fenestrated by side portals. In YnaI, these portals are obstructed by aromatic side chains but are still fully hydrated and thus support conductance. For comparison with large-sized channels, we determined the structure of YbiO, which showed larger portals and a wider pore with no GGxGG motif. Further in silico comparison of MscS, YnaI, and YbiO highlighted differences in the hydrophobicity and wettability of their pores and vestibule interiors. Thus, MscS-like channels of different sizes have a common core architecture but show different gating mechanisms and fine-tuned conductive properties.
History
Deposition
Jul 31, 2020
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Header (metadata) release
Nov 25, 2020
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Map release
Nov 25, 2020
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Update
May 1, 2024
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Current status
May 1, 2024
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Protein or peptide: YnaI,Low conductance mechanosensitive channel YnaI
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Supramolecule #1: open-like YnaI in DIBMA treated with LPC
Supramolecule
Name: open-like YnaI in DIBMA treated with LPC / type: complex / ID: 1 / Parent: 0 / Macromolecule list: all Details: YnaI was purified with the detergent DDM and reconstituted into liposomes. After addition of LPC it was extracted using DIBMA co-polymer.
Cryogen name: ETHANE / Chamber humidity: 90 % / Chamber temperature: 277.15 K / Instrument: FEI VITROBOT MARK IV
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: FEI FALCON III (4k x 4k) / Detector mode: COUNTING / Number real images: 4161 / Average exposure time: 63.0 sec. / Average electron dose: 70.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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