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

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. Although bioengineering of GVs is rapidly progressing, it is hindered by our limited knowledge about their basic structure and assembly. 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. We extend our study with biochemistry and computational modeling to corroborate our model and explore its implications for GV engineering. Together, our results help explain the remarkable mechanical properties of GVs and their ability to adopt different diameters and shapes.