Nucleotide-driven packaging of a singlet oxygen generating porphyrin in an icosahedral virus

Abstract

Results are reported from investigations of the interactions between MS2 bacteriophages and a cationic porphyrin with potential use in photodynamic therapy. Based on the naturally strong binding between porphyrins and nucleic acids, it is suggested that this non-enveloped capsid could act as a self-loading, nanoscale carrier of porphyrins. By applying size exclusion chromatography in conjunction with UV-vis and fluorescence spectroscopy, it is demonstrated that approximately 250 porphyrin molecules could associate and co-elute with a single capsid. Additionally, there is an observed red shift in the Soret peak of the porphyrin, indicating that the majority of the cationic porphyrin is capable of interacting with RNA on the interior of the capsid. It is also observed that removal of RNA from the interior of the MS2 capsid significantly reduces loading capacity of the porphyrin. Furthermore, MS2 bacteriophages loaded with porphyrins were shown to photogenerate singlet oxygen. These findings suggest that icosahedral viruses, such as MS2 bacteriophages, are able to function as self-packaging "nanoscale containers" and efficiently load cationic porphyrins, with potential benefits in areas such as targeted photodynamic therapy.