When the scientists examined the protein, now dubbed Tad1, they found that it captures the signaling molecule immediately after it is produced by the TIR protein. “It was as if the protein quickly swallowed the molecule, not letting the immune system get even a glimpse of it,” Sorek says. “This kind of immune evasion mechanism was never seen in any known virus.”
The group then realized that if the molecule is locked inside the phage protein, they might be able to “see” it by looking within the structure of the protein. Together with their collaborators from Harvard, Prof. Philip Kranzusch and Allen Lu, the team was able, via crystallography, to determine the spatial structure and chemical composition of the molecule. “We have sought this mysterious immune molecule for several years now,” muses Sorek. “Ironically, we couldn’t have found it without an assist from the phage.”