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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.

Crystallization is recognized among structural biologists as a necessary process before three-dimensional structure can be solved at an atomic level. Crystallization has a dose of mysticism among protein chemist. Some treats it as an “art” and others as “black magic”. These concepts aroused from a limited knowledge in the physical chemistry of proteins in solution. Crystallization appears only in a metastable state. To define crystallization conditions the experiments are guided either by a chance search or by dedicated factorial design. Here we will briefly describe a factorial design method to rationally approach the metastable state. In summary, there is nothing mysterious in crystallization of biological macromolecules, and the success can often be achieved within a limited number of experiments.