Structure of the sodium pump
Ion transport ATPases are enzymes with many critical functions in the body. The Membrane Biology Lab does research on the fundamental structure and biology of two ATPases and their specific regulators.
Kathleen J. Sweadner, PhD
Dystonia is a movement disorder characterized by uncontrolled, twisting movements, and it can be devastating in its worst forms. The sodium pump, Na,K-ATPase, plays critical roles in regulating nervous system activity, and so it came as no surprise that mutations in some ATPase genes caused seizures and other epilepsy-related disorders. It was more of a surprise that mutations in the neuron-specific form of the ATPase causes a dystonia that is brought on by stressful events: Rapid-onset dystonia parkinsonism (RDP).
A mouse model of the disease with one copy of the gene knocked out had mild motor problems and enhanced sensitivity to stress. However, it did not develop dystonia. Current research is aimed to produce a Na,K-ATPase mutant mouse with greater sensitivity and clear symptoms, and to understand how stress can trigger an irreversible change in motor system control mechanisms. We are also characterizing a new spontaneous mutant mouse that exhibits dystonia, to use for investigating treatment options.
Scientists in this department did some of the original work back in the 1960s and 1980s showing that an ATPase was critical for the secretion of CSF. Hydrocephalus is usually caused by structural defects that block the flow of CSF out of the brain, and currently-available drugs can temporarily slow down the secretion while surgeons prepare to install a shunt to drain it. This lab discovered that phospholemman (FXYD1) regulates the ATPase in CSF secretion. The current research is to understand how the regulation is controlled and whether the regulation can be enhanced. A knockout mouse and a hydrocephalic mouse are being used to investigate both the molecular mechanisms and the physiology.
Molecular modeling of protein structure is a useful tool for understanding how proteins such as ATPases interact with their environment and how mutations achieve their effects. The availability of atomic structures of ATPases and some of their regulators allows this lab to develop hypotheses and predictive models of regulatory protein-protein interactions, using computers. Massachusetts General Hospital maintains a distributed computer network for computation-intensive molecular modeling used in this lab.
Finally, when using mutant mice, sometimes problems develop that lead to unforeseen new discoveries. A FXYD2 knockout mouse was expected to have kidney symptoms and to have greater sensitivity to stress, but the mouse proved to be very difficult to breed and had unpredictable random deaths. Persistent detective work led to the discovery that it has pancreatic islet cell abnormalities, and the observations may lead to beneficial strategies for treatment of diabetes.
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