Published May 4, 2023 | Published + Supplemental Material
Journal Article Open

Structure of Anabaena flos-aquae gas vesicles revealed by cryo-ET

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Abstract

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 cryoelectron 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. 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.

Additional Information

© 2023 The Author(s). Published by Elsevier. Under a Creative Commons license. Attribution 4.0 International (CC BY 4.0). 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 National Institutes of Health 1S10OD02001301. This work was supported by the National Institutes of Health (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. M.G.S. is a Howard Hughes Medical Institute Investigator. 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. Data and code availability: The unprocessed tilt series used for the data analysis are available upon request. Representative tomograms for Ana, Mega, and Halo GVs have been deposited in the Electron Microscopy Data Bank under accession codes EMDB: EMD-29922, EMD-29925, EMD-29924, EMD-29923. Subtomogram averages for native Ana and AnaS GV shell have been deposited in EMDB under accession codes EMD-29921 and EMD-29916, respectively. The integrative model of Ana GvpA/GvpC has been deposited in the Protein Data Bank (PDB): 8GBS. The XLMS data have been deposited to the ProteomeXchange Consortium with the dataset identifier PXD038631. The code for ultrasound data collection and processing is available upon request. The authors declare no competing interests.

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Created:
August 22, 2023
Modified:
December 22, 2023