News & Events

When

Date - April 24, 2019
1:00 pm - 2:00 pm

What

PhD Defense
Talk Title: Investigating the Biosynthesis of the β-Branch Found in the Polyketide Difficidin Isolated from Bacillus amyloliquefaciens
Advisor: Dr. Jason Reddick

Abstract:

Difficidin is a polyketide antimicrobial macrolide isolated from strains of Bacillus amyloliquefaciens. Although most of the difficidin structure is made by conventional polyketide synthase (PKS), it also contains a small structural feature that is not fully understood. This novel structure comprises a “β-branch” group which is unusual because it is a disubstituted exocylic olefin that is likely thermodynamically unstable compared to the tri-substituted β-branching groups found in other polyketides.  Our hypothesis is that this unusual di-substituted β-branch is generated by enzymes encoded in the Bacillus amyloliquefaciens genome which catalyze steps similar to the pksX cluster found in Bacillus subtilis which generates the tri-substituted β-branch found in bacillaene.  Using mass spectrometry, we reconstituted the later steps of the biosynthesis of the difficidin β-branch, starting with a hydroxymethylglutaryl (HMG) group tethered to the acyl carrier di-domain of the modular polyketide synthase, DfnJ. We were also able to reconstitute early steps of the difficidin β-branch biosynthetic pathway involving the construction of the acetyl-DfnX substrate that provides the extra carbon of the β-branch.  We will report on these findings as well as our ongoing efforts to complete the reconstitution of this pathway involving the reaction of acetyl-DfnX with an acetoacetyl group tethered to the acyl carrier di-domain of DfnJ. Once we reconstitute this pathway we will then be able to study how the difficidin system constructs the unusual di-substituted β-branch.