A Generic Self-Assembly Process in Microcompartments and Synthetic Protein Nanotubes

Area of Science:

• Structural Biology
• Biochemistry
• Nanotechnology

Background:

• Bacterial microcompartments (BMCs) are protein shells encapsulating metabolic pathways.
• Shell proteins like PduA and PduB form these structures, but their precise orientation is key to function.
• Understanding protein self-assembly is crucial for creating novel nanomaterials.

Purpose of the Study:

• To determine the orientation of PduA and PduB shell proteins within bacterial microcompartments and synthetic nanotubes.
• To elucidate the self-assembly principles governing protein nanotube formation.
• To provide insights for engineering protein nanotubes for biotechnological applications.

Main Methods:

• Crystallography to analyze PduA and PduB structures.
• Self-assembly experiments to form synthetic protein nanotubes.
• Structural modeling and experimental validation of protein orientation in nanotubes and in vivo microcompartments.

Main Results:

• PduA hexamers and PduB trimers self-assemble into nanotubes.
• In both 20 nm (PduA) and 63 nm (PduB) nanotubes, the concave surface of the protein subunits faces outward.
• This conserved orientation optimizes subunit interactions and minimizes steric hindrance during assembly.

Conclusions:

• The outward-facing concave surface is a conserved feature in PduA and PduB nanotubes, indicating a generic assembly mechanism.
• This finding reveals fundamental principles of protein self-assembly into ordered nanostructures.
• The understanding of protein orientation and assembly is critical for designing and engineering protein nanotubes for future biotechnological uses.