Structure and heterogeneity of a highly cargo-loaded encapsulin shell

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Encapsulins are self-assembling protein nanocompartments found in bacteria and archaea.
• They play roles in oxidative stress resistance, iron storage, and sulfur metabolism.
• Encapsulin shells have icosahedral symmetry and encapsulate specific enzymes via targeting peptides.

Purpose of the Study:

• To determine the cryo-electron microscopy (cryo-EM) structure of a T3 encapsulin shell from Myxococcus xanthus.
• To investigate the structural heterogeneity of highly cargo-loaded encapsulin shells.
• To analyze the binding mode of targeting peptides to the encapsulin shell interior.

Main Methods:

• Heterologous production of T3 encapsulin from Myxococcus xanthus.
• Cryo-electron microscopy (cryo-EM) at 2.53 Å resolution.
• Analysis of structural heterogeneity and cargo-shell interactions.

Main Results:

• Determined the high-resolution cryo-EM structure of a T3 encapsulin shell.
• Observed distorted and aberrant shells due to high cargo loading and steric clashes.
• Identified both ionic and hydrophobic interactions mediating targeting peptide binding.

Conclusions:

• High cargo loading can lead to structural defects in encapsulin shells.
• The determined structure reveals the molecular basis of cargo encapsulation.
• Findings provide a foundation for engineering encapsulins for biomedical and biotechnological uses.