Single-particle cryo-EM analysis of the shell architecture and internal organization of an intact α-carboxysome

Structure. 2023 Jun 1;31(6):677-688.e4. doi: 10.1016/j.str.2023.03.008. Epub 2023 Apr 3.

Abstract

Carboxysomes are proteinaceous bacterial microcompartments that sequester the key enzymes for carbon fixation in cyanobacteria and some proteobacteria. They consist of a virus-like icosahedral shell, encapsulating several enzymes, including ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), responsible for the first step of the Calvin-Benson-Bassham cycle. Despite their significance in carbon fixation and great bioengineering potentials, the structural understanding of native carboxysomes is currently limited to low-resolution studies. Here, we report the characterization of a native α-carboxysome from a marine cyanobacterium by single-particle cryoelectron microscopy (cryo-EM). We have determined the structure of its RuBisCO enzyme, and obtained low-resolution maps of its icosahedral shell, and of its concentric interior organization. Using integrative modeling approaches, we have proposed a complete atomic model of an intact carboxysome, providing insight into its organization and assembly. This is critical for a better understanding of the carbon fixation mechanism and toward repurposing carboxysomes in synthetic biology for biotechnological applications.

Keywords: carboxysome; cryo-EM; cyanobacteria; photosynthesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Cryoelectron Microscopy
  • Cyanobacteria*
  • Organelles / metabolism
  • Photosynthesis
  • Ribulose-Bisphosphate Carboxylase* / chemistry
  • Ribulose-Bisphosphate Carboxylase* / metabolism

Substances

  • Ribulose-Bisphosphate Carboxylase
  • Bacterial Proteins