Plant pathogenic Pseudomonas syringae produce the hydroxy-β-lactam antimetabolite
tabtoxinine-β-lactam (TβL) as a time-dependent inactivating glutamine analogue of plant
glutamine synthetases. The producing pseudomonads use multiple modes of self-protection,
two of which are characterized in this study. The first is the dipeptide ligase TblF which
converts tabtoxinine-β-lactam to the TβL-Thr dipeptide known as tabtoxin. The dipeptide is
not recognized by glutamine synthetase. This represents a Trojan Horse strategy: the …