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Updated: Jun 18, 2026

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells
Published on: December 13, 2016
Effective charge saturation in ferritin cages
Takumi Kuwata1, Yuusuke Murakami1, Daisuke Sato1
1Department of Biosciences, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo, 192-8577, Japan.
Abstract:
Ferritins are proteins consisting of 24 subunits that make a spherical cage structure. We prepared a series of net-charge mutants of Escherichia coli and Pseudo-nitzschia multiseries ferritins (EcFtn and PmFtn, respectively) in which glutamate (Glu) and aspartate (Asp) residues located at the outer surface of the cage were substituted with glutamine and asparagine or vice versa. The effective negative charges of mutant proteins were evaluated by nondenaturing polyacrylamide gel electrophoresis and ζ-potential measurement. Surprisingly, the effective negative charges of mutants did not increase when the number of Glu and Asp residues increased, while the effective negative charges decreased as the number of Glu and Asp residues decreased. These results suggest that there is a physical net-charge limit in ferritins, and that EcFtn and PmFtn bear maximally possible negative charges. Amino acid sequence analysis has shown that many bacteria and plant ferritins seem to have nearly maximum negative charges, but animal ferritins have fewer negative charges.
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