Petrobactin biosynthesis: AsbB catalyzes condensation of spermidine with N8-citryl-spermidine and its N1-(3,4-dihydroxybenzoyl) derivative

The AsbB enzyme, which is involved in the biosynthesis of the virulence-conferring siderophore petrobactin in Bacillus anthracis, is shown to catalyze efficient ATP-dependent condensation of spermidine, but not N(1)-(3,4-dihydroxbenzoyl)-spermidine, with N(8)-citryl-spermidine or N(1)-(3,4-dihydroxbenzoyl)-N(8)-citryl-spermidine, suggesting that N(1)-(3,4-dihydroxbenzoyl)-spermidine is very unlikely to be a significant intermediate in petrobactin biosynthesis, contrary to previous suggestions.