Formation and characterization of acyl carrier protein-linked polyketide synthase extender units

Polyketide natural products are assembled by the condensation of an initiating precursor, or starter unit, with a series of additional precursors referred to as extender units. While there are a number of polyketide synthase starter units, there are currently only seven known polyketide synthase extender units. Polyketide synthase extender units thioesterified to coenzyme A have been known for some time; however, polyketide synthase extender units thioesterified to acyl carrier proteins (ACPs) have been identified only recently. Two of them, (2R)-hydroxymalonyl-ACP and (2S)-aminomalonyl-ACP, are found in the biosynthetic pathway of the antibiotic zwittermicin A in Bacillus cereus UW85. The focus of this chapter is the in vitro formation of (2R)-hydroxymalonyl-ACP and (2S)-aminomalonyl-ACP and the characterization of these extender units using high performance liquid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry.