Also if anyone knows any good tattoo artists in Seattle, let me know because I've been sitting a few more science tattoo ideas 👀

It turns out that Nip binds specifically to the TIR domain of SpbK, which likely prevents TIR domain interactions. Interestingly, we found that Nip binding to SpbK did not prevent SpbK from binding to YonE! Thus, Nip prevents effector function rather than preventing recognition of phage infection.

Finally, after discovering that an SPbeta-like phage, Phi3T (which has an identical copy of yonE) was able to evade SpbK anti-phage defense, we found a counter-defense gene in Phi3T that is responble for immune evasion. We called the protein Nip for NADase inhibitor from Phi3T.

Next, we determined that YonE, the SPbeta portal protein, activates SpbK via a direct interaction. Using CoIP experiments and AlphaFold modeling, we suspect the SpbK N-terminal region is reponsible for interacting with YonE and facilitates TIR domain interactions that lead to NAD depletion.

We first wondered how SpbK caused abortive infection during infection by SPbeta. SpbK has a TIR domain, which is known to degrade NAD in other systems, and thus we determined that this NAD depletion occurs here as well and that the NAD depletion was dependent on a functional TIR domain.