| 内容提要: |
The amino acid selenocysteine (Sec) has received a lot of attention as a potential anti-cancer drug. However, its broad cytotoxicity limits its therapeutic usefulness. Thus, Sec is an attractive candidate for targeted drug delivery, but delivery vehicles for Sec are lacking. Here, we demonstrate that the capsid formed by Aquifex aeolicus lumazine synthase (AaLS) can act as a nanocarrier for Sec. A previously reported variant of AaLS (AaLS-IC), which contains a single cysteine per subunit that projects into the capsid interior, was modified by reaction with selenocystine to generate a selenosulfide conjugate between the capsid and selenocysteine (AaLS-IC-Sec). Each AaLS-IC-Sec capsid contains approximately 48 selenocysteines, and efficient loading requires placement of the reactive cysteine inside of the protein capsid. Encapsulated Sec can be quantitatively released from the capsid by common reducing agents, such as GSH or DTT, with a half-time of ~3 h. For four of the six cell lines tested, cell viability measurements indicated that AaLS-IC-Sec can go into the cells and release Sec in a toxic form. Fluorescence microscopy experiments revealed an intriguing correspondence between the cytotoxicity of AaLS-IC-Sec and the intracellular trafficking of the AaLS capsid. Cells that do not take up the capsid are insensitive to AaLS-IC-Sec. Moderately and highly sensitive cells accumulate the AaLS capsid in the cytoplasm and nucleus, respectively. Taken together, this study provides a promising foundation for the development of novel systems for the delivery of Sec into cells. |