Functional Characterization and Expression of Molluscan Detoxification Enzymes and Transporters Involved in Dietary Allelochemical Resistance

Kristen E. Whalen, Ph.D., 2008
Mark Hahn, Advisor

The processes underlying dietary allelochemical tolerance are likely mediated, in part, by biochemical resistance mechanisms that have evolved under the selective pressure of host chemical defenses. Although many have invoked this hypothesis to explain the variation in marine consumer tolerance, few studies have examined the enzymatic diversity and corresponding metabolism of dietary allelochemicals.
Molecular and proteomic techniques identified both allelochemically-responsive cytochrome P450s (CYPs), and constitutively expressed glutathione S-transferases (GSTs) and ABC transporters in Cyphoma gibbosum digestive glands. Inhibition of Cyphoma GST activity by gorgonian extracts and selected allelochemicals (i.e., prostaglandins) indicated that gorgonian diets contain substrates for molluscan detoxification enzymes. Enzymatic studies with snail microsomes and recombinant CYPs suggested those Cyphoma enzymes most closely related to vertebrate fatty acid hydroxylating enzymes may contribute to the detoxification of ichthyodeterrent cyclopentenone prostaglandins found in abundance in selected gorgonian species. Finally, the presence and activity of multixenobiotic resistance transporters in Cyphoma and the co-occuring specialist nudibranch, Tritonia hamnerorum, suggests these efflux transporters could function as a first line of defense against dietary intoxication. Together, these results suggest marine consumers that regularly exploit allelochemical-rich prey have evolved both general (GST and ABC transporters) and allelochemical-specific (CYP) detoxification mechanisms to tolerate prey chemical defenses.