Structural Analysis Revealed the Interaction of Cardenolides from Calotropis procera with Na+/K+ ATPases from Herbivores

Background: The herbivores Danaus plexippus (Lepidoptera), Oncopeltus fasciatus, and Aphis nerii (Hemiptera) are special insects that feed on Calotropis procera (Apocynaceae) (Sodom Apple). At least 35 chemically distinct cardenolides have been reported in C. procera. Objective: We aimed to evaluate the interaction between cardenolides and Na+/K+ ATPases from herbivores. Methods: The Na+/K+ ATPases from these insects were modeled, and docking studies were performed involving cardenolides from C. procera. Results: The replacement of serine in sensitive Na+/K+ ATPase by histidine, phenylalanine, and tyrosine in the structures examined suggested spatial impairment caused by interaction, probably making the herbivorous insects resistant against the cardenolides of C. procera. In addition, the ability of the insects to avoid cardenolide toxicity was not correlated with cardenolide polarity. Therefore, the plant fights predation through molecular diversity, and the insects, regardless of their taxonomy, face this molecular diversity through amino acid replacements at key positions of the enzyme targeted by the cardenolides. Conclusion: The results show the arsenal of chemically distinct cardenolides synthesized by the C. procera.