Subcellular localization of dinoflagellate polyketide synthases and fatty acid synthase activity

Frances M Van Dolah; Mackenzie L Zippay; Laura Pezzolesi; Kathleen S Rein; Jillian G Johnson; Jeanine S Morey; Zhihong Wang; Rossella Pistocchi

doi:10.1111/jpy.12120

Subcellular localization of dinoflagellate polyketide synthases and fatty acid synthase activity

J Phycol. 2013 Dec;49(6):1118-27. doi: 10.1111/jpy.12120. Epub 2013 Nov 5.

Authors

Frances M Van Dolah^{1

2}, Mackenzie L Zippay^{1

2}, Laura Pezzolesi³, Kathleen S Rein⁴, Jillian G Johnson^{1

2}, Jeanine S Morey¹, Zhihong Wang¹, Rossella Pistocchi³

Affiliations

¹ Marine Biotoxins Program, NOAA Center for Coastal Environmental Health and Biomolecular Research, Charleston, South Carolina, 29412, USA.
² Marine Biomedical and Environmental Sciences, Medical University of South Carolina, Charleston, South Carolina, 29412, USA.
³ Interdepartmental Research Centre for Environmental Science (CIRSA), University of Bologna, Ravenna, 48123, Italy.
⁴ Department of Chemistry and Biochemistry, Florida International University, Miami, Florida, 33199, USA.

PMID: 27007632
DOI: 10.1111/jpy.12120

Abstract

Dinoflagellates are prolific producers of polyketide secondary metabolites. Dinoflagellate polyketide synthases (PKSs) have sequence similarity to Type I PKSs, megasynthases that encode all catalytic domains on a single polypeptide. However, in dinoflagellate PKSs identified to date, each catalytic domain resides on a separate transcript, suggesting multiprotein complexes similar to Type II PKSs. Here, we provide evidence through coimmunoprecipitation that single-domain ketosynthase and ketoreductase proteins interact, suggesting a predicted multiprotein complex. In Karenia brevis (C.C. Davis) Gert Hansen & Ø. Moestrup, previously observed chloroplast localization of PKSs suggested that brevetoxin biosynthesis may take place in the chloroplast. Here, we report that PKSs are present in both cytosol and chloroplast. Furthermore, brevetoxin is not present in isolated chloroplasts, raising the question of what chloroplast-localized PKS enzymes might be doing. Antibodies to K. brevis PKSs recognize cytosolic and chloroplast proteins in Ostreopsis cf. ovata Fukuyo, and Coolia monotis Meunier, which produce different suites of polyketide toxins, suggesting that these PKSs may share common pathways. Since PKSs are closely related to fatty acid synthases (FAS), we sought to determine if fatty acid biosynthesis colocalizes with either chloroplast or cytosolic PKSs. [(3) H]acetate labeling showed fatty acids are synthesized in the cytosol, with little incorporation in chloroplasts, consistent with a Type I FAS system. However, although 29 sequences in a K. brevis expressed sequence tag database have similarity (BLASTx e-value <10(-10) ) to PKSs, no transcripts for either Type I (cytosolic) or Type II (chloroplast) FAS are present. Further characterization of the FAS complexes may help to elucidate the functions of the PKS enzymes identified in dinoflagellates.

Keywords: Coolia monotis; Karenia brevis; Ostreopsis cf. ovata; brevetoxin; dinoflagellates; fatty acid synthase; palytoxin; polyketide synthase.