Journal: Nat Struct Mol Biol / Year: 2023 Title: Molecular mechanisms of inorganic-phosphate release from the core and barbed end of actin filaments. Authors: Wout Oosterheert / Florian E C Blanc / Ankit Roy / Alexander Belyy / Micaela Boiero Sanders / Oliver Hofnagel / Gerhard Hummer / Peter Bieling / Stefan Raunser / Abstract: The release of inorganic phosphate (P) from actin filaments constitutes a key step in their regulated turnover, which is fundamental to many cellular functions. The mechanisms underlying P release ...The release of inorganic phosphate (P) from actin filaments constitutes a key step in their regulated turnover, which is fundamental to many cellular functions. The mechanisms underlying P release from the core and barbed end of actin filaments remain unclear. Here, using human and bovine actin isoforms, we combine cryo-EM with molecular-dynamics simulations and in vitro reconstitution to demonstrate how actin releases P through a 'molecular backdoor'. While constantly open at the barbed end, the backdoor is predominantly closed in filament-core subunits and opens only transiently through concerted amino acid rearrangements. This explains why P escapes rapidly from the filament end but slowly from internal subunits. In a nemaline-myopathy-associated actin variant, the backdoor is predominantly open in filament-core subunits, resulting in accelerated P release and filaments with drastically shortened ADP-P caps. Our results provide the molecular basis for P release from actin and exemplify how a disease-linked mutation distorts the nucleotide-state distribution and atomic structure of the filament.
Name: actin-phalloidin complex / type: complex / ID: 1 / Parent: 0 / Macromolecule list: #1 Details: Actin was purified as monomer from bovine thymus. Short filaments were reconstituted in vitro to obtain the barbed end structure.
Details: 10 mM imidazole pH 7.1, 100 mM KCl, 2 mM MgCl2 and 1 mM EGTA
Grid
Model: Quantifoil R2/1 / Material: COPPER / Mesh: 300 / Support film - Material: CARBON / Support film - topology: HOLEY / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 90 sec.
Vitrification
Cryogen name: ETHANE-PROPANE / Chamber humidity: 100 % / Chamber temperature: 286 K / Instrument: FEI VITROBOT MARK IV
Details
Sample was directly collected from size-exclusion chromatography fractions.
-
Electron microscopy
Microscope
FEI TALOS ARCTICA
Details
Microsope alignment was performed using SHERPA (Thermo Fisher)
Image recording
Film or detector model: FEI FALCON III (4k x 4k) / Detector mode: INTEGRATING / Number grids imaged: 1 / Number real images: 1316 / Average exposure time: 4.0 sec. / Average electron dose: 56.0 e/Å2
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
Applied symmetry - Point group: C1 (asymmetric) / Resolution.type: BY AUTHOR / Resolution: 3.59 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: cryoSPARC (ver. 3.3.2) Details: Performed in CryoSPARC. All barbed end particles were isolated from from other particles that represented pointed end and filament core. Number images used: 43618
Initial angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 3.3.2) / Details: First refinement performed in CryoSPARC.
Final angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 3.3.2) Details: Final refinement performed in CryoSPARC. The barbed end structure was refined as a single particle without applying any restraints.
Final 3D classification
Number classes: 2 / Software - Name: cryoSPARC (ver. 3.3.2)
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