Structure of Anabaena flos-aquae gas vesicles revealed by cryo-ET
Gas vesicles (GVs) are gas-filled protein nanostructures employed by several species of bacteria and archaea as flotation devices to enable access to optimal light and nutrients. The unique physical properties of GVs have led to their use as genetically-encodable contrast agents for ultrasound and MRI. Currently, however, the structure and assembly mechanism of GVs remain unknown. Here we employ cryo-electron tomography to reveal how the GV shell is formed by a helical filament of highly conserved GvpA subunits. This filament changes polarity at the center of the GV cylinder—a site that may act as an elongation center. High-resolution subtomogram averaging reveals a corrugated pattern of the shell arising from polymerization of GvpA into a β-sheet. The accessory protein GvpC forms a helical cage around the GvpA shell, providing structural reinforcement. Together, our results help explain the remarkable mechanical properties of GVs and their ability to adopt different diameters and shapes.
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license. Version 1 June 21, 2022; Version 2 - July 12, 2022. The authors are grateful to Catherine Oikonomou for helpful editorial comments. We thank Songye Chen for assistance with tomography data collection. Electron microscopy was performed in the Beckman Institute Resource Center for Transmission Electron Microscopy at Caltech. The Proteome Exploration Laboratory (PEL) is supported by the Beckman Institute and NIH 1S10OD02001301. This work was supported by the National Institutes of Health (grant R01-AI127401 to G.J.J. and R01-EB018975 to M.G.S.) and the Caltech Center for Environmental Microbial Interactions (CEMI). Related research in the Shapiro Laboratory is supported by the Packard Foundation, the Chan Zuckerberg Initiative and the Heritage Medical Research Institute. Author Contributions: P.D. conceived experiments, prepared samples, acquired and analyzed data, performed data exploration, drafted the manuscript, and prepared the figures. L.A.M initiated the project and collected data for Mega GVs. R.C.H performed mutation screening for GvpA and participated in initial sample preparation and optimization for Mega GVs. H.S. performed finite element simulation and analyzed data. T-Y.W performed XLMS experiments and analyzed the data. D.M expressed and purified GV samples. G.L. participated in initial sample preparation and optimization for Mega GVs. T-F.C. supervised XLMS experiments. All authors participated in correction of the manuscript. M.G.S. participated in guidance, experimental design, funding, and correction/advising on writing the manuscript. G.J.J participated in guidance, experimental design, funding, and correction/advising on writing the manuscript. The authors declare no competing interests. Data Availability: Cryo-ET density maps and GvpA/GvpC integrative model are available on Zenodo zenodo.org/record/6820642#.Ys0aROzMKw1
Submitted - 2022.06.21.496981v2.full.pdf
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