Decoding the absolute stoichiometric composition and structural plasticity of α-carboxysomes

Abstract

Carboxysomes are anabolic bacterial microcompartments that play an essential role in carbon fixation in cyanobacteria and some chemoautotrophs. This self-assembling organelle encapsulates the key CO2-fixing enzymes, Rubisco, and carbonic anhydrase using a polyhedral protein shell that is constructed by hundreds of shell protein paralogs. The -carboxysome from the chemoautotroph Halothiobacillus neapolitanus serves as a model system in fundamental studies and synthetic engineering of carboxysomes. Here we adopt a QconCAT-based quantitative mass spectrometry to determine the absolute stoichiometric composition of native -carboxysomes from H. neapolitanus. We further performed an in-depth comparison of the protein stoichiometry of native and recombinant -carboxysomes heterologously generated in Escherichia coli to evaluate the structural variability and remodeling of -carboxysomes. Our results provide insight into the molecular principles that mediate carboxysome assembly, which may aid in rational design and reprogramming of carboxysomes in new contexts for biotechnological applications.