Identification and biosynthesis of a novel thymidine hypermodification Na-dapT in Acinetobacter baumannii phage SH-Ab 15599

Recent discoveries of aGPT-Pplase2-catalyzed novel thymidine hypermodifications reveal a broader enzymatic and chemical diversity in phage DNA modification systems. However, the diversity of thymidine hypermodification in other bacteriophages remains largely unexplored.

Here we discovered a novel thymidine hypermodification, Na-dapT, in the Acinetobacter baumannii phage SH-Ab 15599, and elucidated its biosynthetic pathway, including the key diamine DNA transferase (DADT, formerly aGPT-Pplase2). DADT utilizes the abundant metabolite 1,3-diaminopropane of host to modify 5hmdU-DNA, exhibiting broad in vitro substrate specificity but a strong in vivo preference for 1,3-diaminopropane. Structural and mutagenesis analyses revealed the molecular basis for substrate recognition and catalysis.