Carrier protein and halogenase selectivity in the biosynthesis of halogenated pyrroles

Natural product biosynthetic pathways often share similar architecture even when they lead to different final products. In polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) enzymatic pathways, the substrate is attached to a carrier protein (CP) while the tailoring enzymes make modifications to yield a final product. The CP may therefore have a role in determining what enzymes act on the substrate, influencing the final product’s chemistry. In this study, pyrrole halogenases from several different bacterial species were characterized in vitro to test their ability to halogenate pyrrolyl CPs from four different natural product biosynthetic pathways. The reactions were analyzed via mass spectrometry to determine the halogenation state of the products formed. This study concludes that only some halogenases can act promiscuously on CPs from other pathways. Additionally, there is some modulation in the number of halogenation events between certain CP and halogenase pairs. The selectivity of these halogenase and CP interactions is likely caused by protein-protein interactions, and the structure of the CP/halogenase complex may provide new insights into such interaction.Undergraduat