Present address: Department of Molecular Biology, The University of Bergen, Bergen 5008, Norway.
BIOCHEMICAL CHARACTERIZATION OF PARALYTIC SHELLFISH TOXIN BIOSYNTHESIS IN VITRO1
Article first published online: 16 MAY 2007
© 2007 Phycological Society of America
Journal of Phycology
Volume 43, Issue 3, pages 497–508, June 2007
How to Cite
Kellmann, R. and Neilan, B. A. (2007), BIOCHEMICAL CHARACTERIZATION OF PARALYTIC SHELLFISH TOXIN BIOSYNTHESIS IN VITRO. Journal of Phycology, 43: 497–508. doi: 10.1111/j.1529-8817.2007.00351.x
Received 19 April 2006. Accepted 23 February 2007.
- Issue published online: 16 MAY 2007
- Article first published online: 16 MAY 2007
- Cylindrospermopsis raciborskii;
- in vitro biosynthesis;
- paralytic shellfish toxins;
Saxitoxin (STX) and its analogs are voltage-gated sodium-channel blockers that cause paralytic shellfish poisoning (PSP) and negatively affect human health and seafood industries worldwide. Little is known about the molecular biology of PSP-toxin synthesis. Saxitoxin precursors were identified 25 years ago, and a hypothetical biosynthesis pathway was proposed; however, the correct sequence of reactions and enzymes involved in their catalysis remains to be identified. This study describes the optimization of in vitro biosynthesis of PSP toxins by cellular lysates of the toxic cyanobacterium Cylindrospermopsis raciborskii (Wołosz.) Seenaya et Subbaraju T3 and the characterization of its biochemical requirements. Enzymes involved in PSP-toxin synthesis are located in the cytosol. The molecular components of in vitro biosynthesis reactions could not be completely defined because of the requirement of an unknown cofactor. Evidence is presented that supports the previous suggestion that STX biosynthesis involves a Claisen condensation between arginine and acetate. In addition, carbamoyl phosphate was identified as a likely precursor for carbamated PSP toxins. Predictions have been made regarding the enzymes that may be involved in the biosynthesis of PSP toxins. These included class II aminotransferase; nonheme iron oxygenase, containing flavin, and possibly ferredoxin, as the prosthetic groups; and an O-carbamoyltransferase. On the other hand, the involvement of cytochrome P450 monooxygenase was excluded.