Carboxysome Shell Protein CcmK2 Assembles into Monodisperse and pH-Reversible Microparticles

Area of Science:

• Biotechnology
• Protein Engineering
• Materials Science

Background:

• Protein-based compartments offer advantages like biodegradability and biocompatibility over synthetic particles.
• Bacterial microcompartments (BMCs) are self-assembling protein organelles with potential for biotechnological applications.
• Engineering BMC shell proteins into synthetic nanoreactors and scaffolds is an active area of research.

Purpose of the Study:

• To develop a method for *in vitro* assembly of single-component monodisperse microparticles using only CcmK2.
• To investigate the controlled assembly of CcmK2 into solid microparticles.
• To explore the potential of CcmK2 particles as building blocks in biotechnology.

Main Methods:

• Utilized CcmK2, the major hexameric shell protein of the β-carboxysome BMC.
• Employed *in vitro* assembly techniques.
• Conducted high-resolution imaging and biochemical characterization.

Main Results:

• Achieved controlled assembly of single-component CcmK2 into monodisperse solid microparticles.
• Revealed CcmK2 particles are assemblies of radially clustered nanotubes via imaging.
• Determined pH as a key regulator of particle size and disassembly through biochemical analysis.

Conclusions:

• CcmK2 protein can self-assemble into precisely controlled, monodisperse solid microparticles.
• These CcmK2 particles represent a novel protein-based material for biotechnology.
• The findings enable future applications leveraging these engineered protein compartments.