Pore dynamics and asymmetric cargo loading in an encapsulin nanocompartment

Area of Science:

• Structural biology
• Biochemistry
• Protein engineering

Background:

• Encapsulins are protein nanocompartments that encapsulate various enzymes.
• Ferritin is a family of decameric, iron-storage proteins with a ferritin-like structure.
• Understanding the encapsulin-ferritin interaction is key for protein encapsulation applications.

Purpose of the Study:

• To elucidate the structural relationship between the Haliangium ochraceum encapsulin shell and its encapsulated ferritin cargo.
• To investigate the dynamic behavior of the encapsulin shell's pore structure.

Main Methods:

• Asymmetric single-particle cryo-electron microscopy (cryo-EM) for structural determination.
• Hydrogen/deuterium exchange mass spectrometry (HDX-MS) for dynamic analysis of the encapsulin shell.

Main Results:

• Four ferritin decamers were observed in a tetrahedral arrangement within the icosahedral encapsulin shell, creating a symmetry mismatch.
• Ferritin cargo was found to be offset from the inner surface of the encapsulin shell.
• HDX-MS data revealed dynamic opening of the encapsulin shell's fivefold pore through A-domain movement.

Conclusions:

• The study provides high-resolution structural insights into the encapsulin-ferritin complex.
• Understanding the dynamic pore behavior facilitates engineering efforts for altered encapsulin shell permeability.
• These findings accelerate the development of encapsulins for encapsulating heterologous cargo proteins.