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Brittany Kiel

Posted on February 17, 2016


Date - February 17, 2016
1:00 pm


Ph.D. Literature Seminar – 751
Title: “Investigating a Novel Pathway for the Biosynthesis of Polyketide β-Branching and the Dual Function of PksJ Encoded by the PksX Cluster Isolated from Bacillus subtilis.”


Bacillaene is a polyene antibiotic that belongs to the Gram positive Bacillaceae family and is biosynthesized by a unique hybrid of polyketide and nonribosomal peptide synthase. By isolating 5 important genes from the PksX cluster that act systematically in its synthesis, researchers have come up with a new pathway for polyketide synthesis in microorganisms that has previously been uncharacterized. A team led by Chrisopher Calderone was able to assign functional roles to the proteins AcpK, PksC, PksL (a double thiolation domain), PksF, PksG, PksH, and PksI through the combination of biochemical and mass spectrometric techniques. This work highlights the ability of mass spectrometry to elucidate the functions of single biosynthetic enzymes. Because of this, researchers were able to discover a mechanism that explains how single-carbon β-branches can be inserted into polyketide-like structures.

Dihydrobacillaene is the initial product of the PksX cluster and is converted to bacillaene in the penultimate step of its synthesis before being released as a linear compound. Previous work has shown the dihydrobacillaene assembly line to be an abundant source of unusual biochemistry. Little precedent existed for α-hydroxyacyl units in PKS/NRPs until Calderone investigated further, finding that dihydrobacillaene/bacillaene possessed a unique dual-function ketoreductase domain. This domain is found in PksJ and acts as a canonical β-KR and a noncanonical α-KR dictating the structures of the intermediates found on its double thiolation domain.

Calderone’s focal point of both papers features strange chemistry occurring at double thiolation domains. His work contributed to the understanding of new chemistry that had previously been unknown, and opened up the gate for further research into the capabilities of double thiolation domains.