Fold DAT right,
sleepless flies!

Published January 05 2016

Cover A Drosophila brain (blue) with the sleep-regulation center (green). The white ribbondiagram is the structure of the dopamine transporter with the mutation site (red). IMAGE PROVIDED BY MICHAEL FREISSMUTH

In a recent Paper of the Week in the Journal of Biological Chemistry, investigators reported using small molecules to correct the misfolded receptor for the neurotransmitter dopamine and restoring its function in mutant fruit flies that have trouble falling asleep.

Dopamine is a neurotransmitter that plays critical roles in many processes, including movement, memory, cognition and behavior. The dopamine transporter, known as DAT, controls the availability of dopamine in the brain, because it is involved in the movement of dopamine from the synapse into the neuron.

Point mutations in DAT are associated with a rare form of Parkinson’s disease in which the dopamine transporter is deficient. The rare disease primarily affects children of consanguineous couples. These mutations lead to a misfolded DAT. This condition also is known as infantile parkinsonism-dystonia, since the patients typically have problems with movement. Dystonia is characterized by involuntary sustained muscle contractions.

To understand better how a misfolded DAT causes diseases, researchers had developed mutant fruit flies. These flies have a misfolded DAT that can’t reach the brain’s sleep regulation center. As a result, the mutant flies are less sleepy than normal flies.

Endogenous chaperones regulate the efficient folding of proteins. Proper folding also can be brought about by introducing small molecules, a process known as pharmacochaperoning. In this JBC paper, Michael Freissmuth at the Medical University of Vienna in Austria and colleagues set out to see if they could carry out pharmacochaperoning in the mutant sleepless fruit flies and correct the misfolding of DAT. “The ability to restore the function of a misfolded dopamine transporter by a drug is of general interest,” says Freissmuth.

Using a host of molecular dynamic simulations and molecular biology techniques, the investigators established that the sleepless phenotype in flies harboring the mutant DAT indeed was caused by a folding defect in the mutant protein. Treatment of cells in culture with two small molecules, noribogaine and pifithrin-μ, rescued the misfolded protein and resulted in its efficient localization to the membrane surface and dopamine transport. When the investigators treated the mutant flies with one of the two small molecules, the flies slept the same length of time as normal flies because the mutant DAT was able to get to the brain’s sleep-regulation center.

The findings of this study have the potential to have beneficial implications in patients suffering from the rare disease of dopamine transporter deficiency. Freissmuth says, “Dopamine transporter deficiency is a devastating disease. The affected children suffer from a syndrome of dystonia and parkinsonism with rigid limbs. The majority have poor prognosis and die young.” Freissmuth adds that their work has the potential to be translated into a treatment soon.

Kamalika Saha Kamalika Saha is a postdoctoral fellow in medical communications at MedImmune.