Different combinations of insect Na,K-ATPase α- and β-subunits enable fine-tuned adaptation to host plant toxins and tissue specific needs

Background

Cardiac glycosides are known to fatally inhibit the Na,K-ATPase throughout the animal kingdom. Several animals, however, evolved target-site insensitivity by substitutions in the otherwise highly conserved cardiac glycoside binding pocket located on the Na,K-ATPase α-subunit. The minimal functional enzyme consist of an α- and a β-subunit, the latter considered mainly as a chaperone responsible for correct folding and membrane integration. We here analyze resistance to cardiac glycosides and kinetic properties of different Na,K-ATPase α/β-combinations of the large milkweed bug, Oncopeltus fasciatus. These insects have adapted to high concentrations of cardiac glycosides in their food plants via several rounds of Na,K-ATPase gene duplications followed by differential resistance conferring substitutions and subfunctionalization of the enzymes.

Results

To investigate their characteristics we expressed nine combinations of O. fasciatus Na,K-ATPase α/β-sunbunits (three eac...