Multivalent interactions between CsoS2 and Rubisco mediate α-carboxysome formation

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Carboxysomes are bacterial microcompartments central to the CO2-concentrating mechanism.
• They encapsulate the enzyme Rubisco to enhance carbon fixation efficiency.
• Molecular mechanisms of alpha-carboxysome assembly remain poorly understood.

Purpose of the Study:

• To elucidate the protein-protein interactions driving alpha-carboxysome assembly.
• To understand the role of CsoS2 in Rubisco recruitment and carboxysome formation.

Main Methods:

• X-ray structural analysis of Rubisco-CsoS2 complexes.
• Biophysical measurements of binding affinities.
• Studies on the alpha-carboxysome from Halothiobacillus neapolitanus.

Main Results:

• Rubisco directly interacts with the N terminus of CsoS2, an intrinsically disordered protein.
• Specific electrostatic interactions occur between CsoS2 and hexadecameric Rubisco.
• Despite weak individual binding, multivalency via avidity leads to high-affinity Rubisco-CsoS2 interaction.

Conclusions:

• CsoS2 functions as a critical interaction hub in alpha-carboxysome assembly.
• CsoS2 facilitates Rubisco condensation, enabling efficient carboxysome formation.
• Understanding these interactions is key to optimizing bacterial carbon fixation.