Intrinsically disordered CsoS2 acts as a general molecular thread for α-carboxysome shell assembly.

Area of Science:

• Biochemistry
• Structural Biology
• Synthetic Biology

Background:

• Carboxysomes are protein-based organelles crucial for efficient carbon fixation in microorganisms.
• The disordered linker protein CsoS2 is vital for the assembly and function of alpha-carboxysomes.
• The precise mechanism of CsoS2 in carboxysome formation and Rubisco enzyme encapsulation remains incompletely understood.

Purpose of the Study:

• To elucidate the assembly principles of alpha-carboxysome shells using minimal components.
• To determine the structural basis of CsoS2's role in carboxysome assembly and cargo encapsulation.
• To advance the synthetic engineering of carboxysomes for biotechnological purposes.

Main Methods:

• Synthetic engineering of alpha-carboxysome shells with essential components.
• Cryo-electron microscopy (cryo-EM) to determine high-resolution structures.
• Bioinformatic analysis to identify conserved motifs within CsoS2.

Main Results:

• Cryo-EM structures revealed the CsoS2 C-terminus acts as a 'molecular thread' integrating shell proteins.
• A conserved [IV]TG motif in CsoS2 was identified as critical for shell assembly and architecture.
• A general mechanism for CsoS2-mediated carboxysome assembly and encapsulation was proposed.

Conclusions:

• CsoS2's intrinsically disordered C-terminus adopts a structured role as a molecular scaffold.
• The conserved [IV]TG motif is a key determinant of carboxysome structure and assembly.
• This work provides insights for the rational design and synthetic construction of carboxysomes.