Investigating A Multi-Domain Polyketide Synthase in Amphidinium carterae.

Area of Science:

• Marine Biology
• Biochemistry
• Molecular Biology

Background:

• Dinoflagellates are unicellular organisms responsible for harmful algal blooms (HABs).
• These organisms produce potent toxins via polyketide synthase (PKS) pathways.
• The precise mechanisms of dinoflagellate toxin synthesis remain unclear due to pathway complexity.

Purpose of the Study:

• To investigate the actions and expression of PKS proteins in the toxic dinoflagellate *Amphidinium carterae*.
• To elucidate the mechanisms differentiating fat and toxin synthesis pathways.
• To understand the genetic basis of toxin production in dinoflagellates.

Main Methods:

• Utilized cerulenin, a ketosynthase inhibitor, to study acetate incorporation.
• Performed mass spectrometry and collision-induced dissociation on cerulenin-reacted peptides.
• Analyzed multimodular PKS sequences and employed Western blotting to assess protein processing.

Main Results:

• Cerulenin inhibited acetate incorporation into both fats and toxins (amphidinol, sulpho-amphidinol).
• Mass spectrometry confirmed covalent bonding between cerulenin and PKS ketosynthase domains.
• A PKS sequence lacking an AT domain in toxin-producing species suggests *trans*-acting domains and post-transcriptional modification.

Conclusions:

• Dinoflagellate toxin synthesis can be distinguished from fat synthesis despite shared PKS pathways.
• Post-transcriptional processing plays a role in PKS function for toxin production.
• This research provides insight into the molecular mechanisms underlying HABs.