National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
United States
Citation
Journal: Nature / Year: 2024 Title: Mechanisms of actin filament severing and elongation by formins. Authors: Nicholas J Palmer / Kyle R Barrie / Roberto Dominguez / Abstract: Humans express 15 formins that play crucial roles in actin-based processes, including cytokinesis, cell motility and mechanotransduction. However, the lack of structures bound to the actin filament ...Humans express 15 formins that play crucial roles in actin-based processes, including cytokinesis, cell motility and mechanotransduction. However, the lack of structures bound to the actin filament (F-actin) has been a major impediment to understanding formin function. Whereas formins are known for their ability to nucleate and elongate F-actin, some formins can additionally depolymerize, sever or bundle F-actin. Two mammalian formins, inverted formin 2 (INF2) and diaphanous 1 (DIA1, encoded by DIAPH1), exemplify this diversity. INF2 shows potent severing activity but elongates weakly whereas DIA1 has potent elongation activity but does not sever. Using cryo-electron microscopy (cryo-EM) we show five structural states of INF2 and two of DIA1 bound to the middle and barbed end of F-actin. INF2 and DIA1 bind differently to these sites, consistent with their distinct activities. The formin-homology 2 and Wiskott-Aldrich syndrome protein-homology 2 (FH2 and WH2, respectively) domains of INF2 are positioned to sever F-actin, whereas DIA1 appears unsuited for severing. These structures also show how profilin-actin is delivered to the fast-growing barbed end, and how this is followed by a transition of the incoming monomer into the F-actin conformation and the release of profilin. Combined, the seven structures presented here provide step-by-step visualization of the mechanisms of F-actin severing and elongation by formins.
Model: Quantifoil R1.2/1.3 / Material: COPPER / Mesh: 300 / Support film - Material: CARBON / Support film - topology: HOLEY / Support film - Film thickness: 100 / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 120 sec.
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Number real images: 41926 / Average electron dose: 44.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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