The unique self-assembly/disassembly property of Archaeoglobus fulgidus ferritin and its implications on molecular release from the protein cage.
BACKGROUND
In conventional in vitro encapsulation of molecular cargo, the multi-subunit ferritin protein cages are disassembled in extremely acidic pH and re-assembled in the presence of highly concentrated cargo materials, which results in poor yields due to the low-pH treatment. In contrast, Archaeoglobus fulgidus open-pore ferritin (AfFtn) and its closed-pore mutant (AfFtn-AA) are present as dimeric species in neutral buffers that self-assemble into cage-like structure upon addition of metal ions.


METHODS
To understand the iron-mediated self-assembly and ascorbate-mediated disassembly properties, we studied the iron binding and release profile of the AfFtn and AfFtn-AA, and the corresponding oligomerization of their subunits.


RESULTS
Fe(2+) binding and conversion to Fe(3+) triggered the self-assembly of cage-like structures from dimeric species of AfFtn and AfFtn-AA subunits, while disassembly was induced by dissolving the iron core with reducing agents. The closed-pore AfFtn-AA has identical iron binding kinetics but lower iron release rates when compared to AfFtn. While the iron binding rate is proportional to Fe(2+) concentration, the iron release rate can be controlled by varying ascorbate concentrations.


CONCLUSIONS
The AfFtn and AfFtn-AA cages formed by iron mineralization could be disassembled by dissolving the iron core. The open-pores of AfFtn contribute to enhanced reductive iron release while the small channels located at the 3-fold symmetry axis (3-fold channels) are used for iron uptake.


CONCLUSIONS
The iron-mediated self-assembly/disassembly property of AfFtn offers a new set of molecular trigger for formation and dissociation of the protein cage, which can potentially regulate uptake and release of molecular cargo from protein cages.
School of Chemical & Biomedical Engineering, Division of Bioengineering, Nanyang Technological University, 637457, Singapore.
Barindra
B
Sana
Howard Hughes Medical Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Eric
E
Johnson
School of Chemical & Biomedical Engineering, Division of Bioengineering, Nanyang Technological University, 637457, Singapore. Electronic address: SLim@ntu.edu.sg.
Sierin
S
Lim
D019611:Archaeoglobus fulgidus / Q000378:metabolism*; D001205:Ascorbic Acid / Q000378:metabolism; D005293:Ferritins / Q000378:metabolism*; D007700:Kinetics
D005293:Ferritins; D001205:Ascorbic Acid
Binding kinetics; Dissociation; Molecular release; Protein cage; Release kinetics; Self-assembly