Decoding the Absolute Stoichiometric Composition and Structural Plasticity of α-Carboxysomes.

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Carboxysomes are bacterial microcompartments crucial for carbon fixation, encapsulating Rubisco and carbonic anhydrase within a protein shell.
• The α-carboxysome from *Halothiobacillus neapolitanus* is a model system for studying these organelles' assembly and function.
• Understanding carboxysome structure is vital for enhancing biological carbon fixation processes.

Purpose of the Study:

• To determine the stoichiometric composition of native α-carboxysomes from *H. neapolitanus* using quantitative mass spectrometry.
• To compare the protein stoichiometry of native α-carboxysomes with their recombinant counterparts in *E. coli*.
• To evaluate the structural variability and remodeling of α-carboxysomes.

Main Methods:

• Quantitative mass spectrometry (QconCAT approach).
• Biochemistry and enzymatic assays.
• Electron microscopy.
• Heterologous expression in *Escherichia coli*.

Main Results:

• Detailed stoichiometric composition of native α-carboxysomes was elucidated.
• Significant differences in protein stoichiometry were observed between native and recombinant carboxysomes.
• Structural plasticity and potential remodeling mechanisms of carboxysomes were identified.

Conclusions:

• The study provides fundamental insights into the molecular assembly principles of carboxysomes.
• Understanding carboxysome architecture and modularity is key for synthetic biology applications.
• This research paves the way for engineering carboxysomes in new hosts, like plants, to boost cellular metabolism and crop yields.