Sporadic hemiplegic migraine type 2 (SHM2) and
familial hemiplegic migraine type 2 (FHM2) are rare forms of hemiplegic
migraine caused by mutations in the Na(+),K(+)-
ATPase α2 gene. Today, more than 70 different mutations have been linked to SHM2/FHM2, randomly dispersed over the gene. For many of these mutations, functional studies have not been performed. Here, we report the functional characterization of nine SHM2/FHM2 linked mutants that were produced in Spodoptera frugiperda (Sf)9 insect cells. We determined
ouabain binding characteristics, apparent Na(+) and K(+) affinities, and maximum
ATPase activity. Whereas membranes containing T345A, R834Q or R879W possessed
ATPase activity significantly higher than control membranes, P796S, M829R, R834X, del 935-940 ins Ile, R937P and D999H membranes showed significant loss of
ATPase activity compared to wild type
enzyme. Further analysis revealed that T345A and R879W showed no changes for any of the parameters tested, whereas mutant R834Q possessed significantly decreased Na(+) and increased K(+) apparent affinities as well as decreased
ATPase activity and
ouabain binding. We hypothesize that the majority of the mutations studied here influence interdomain interactions by affecting formation of hydrogen bond networks or interference with the C-terminal ion pathway necessary for catalytic activity of Na(+),K(+)-
ATPase, resulting in decreased functionality of astrocytes at the synaptic cleft expressing these mutants.