Molecular studies on the ouabain binding site of the Na+, K+-ATPase in milkweed butterflies

The Na (+), K (+) -ATPase of the Monarch butterfly (Danaus plexippus) is in sensitive to the inhibition by cardiac glycosides due to an amino acid repl acement: histidine instead of asparagine at position 122 of the a-subunit r epresenting the ouabain binding site. By PCR amplification of the DNA seque nce of this site, a PCR product of 270 bp was obtained from DNA extracted f rom Danainae species (Dananus plexippus, D.chrysippus, D.gillipus, D.philen e, D.genutia, Tirumala hamata, Euploea spp., Parantica weiskei, P.melusine) , Sphingidae (Daphnis nerii) and mimics of milkweed butterflies (Hypolimnas missipus, Limenitis archippus and L.arthemis, Nymphalidae). Analysis of th e nucleotide sequences revealed that the single point mutation in the ouaba in binding domain (AAC-Asn for CAC-His) was present only in Danaus plexippu s, but not in the other species investigated. Since these milkweed butterfl ies also store cardenolides, other structural modifications of the Na+, K+- ATPase may have occurred or other strategies of cardenolide tolerance have been developed.