Massachusetts General Hospital

Structure of the sodium pump

Overview

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.

• Mutations in one of the ATPases, a sodium pump, causes dystonia in patients, and the lab is developing a mouse model of the disease for research on treatments
• The sodium pump is also critical for making cerebrospinal fluid, and the lab investigates its role in hydrocephalus, using both mice and the methods of biochemistry and molecular biology. The goal is to control hydrocephalus without surgical shunts
• Another enzyme is a plasma membrane calcium pump, and the lab investigates the structural basis of its regulation by calmodulin
• Mice with defects in ATPase regulators called FXYD proteins were discovered to have problems with either kidney function or insulin production, opening the door to new approaches to hypertension or diabetes research

Kathleen J. Sweadner, PhD

Group Members

• Kathleen J. Sweadner, PhD, Laboratory Director
• Elena Arystarkhova, PhD
• John T. Penniston, PhD
• Bessie Liu
• Cynthia Salazar

Research Projects

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.

Research Positions

There are no available positons at this time.  Please check back at a later date for updates.

Publications

• Case records of the Massachusetts General Hospital. Case 17-2010 - a 29-year-old woman with flexion of the left hand and foot and difficulty speaking.
  Tarsy D, Sweadner KJ, Song PC.
  N Engl J Med. 2010 Jun 10;362(23):2213-9
• Calmodulin wraps around its binding domain in the plasma membrane Ca2+ pump anchored by a novel 18-1 motif.
  Juranic N, Atanasova E, Filoteo AG, Macura S, Prendergast FG, Penniston JT, Strehler EE.
  J Biol Chem. 2010 Feb 5;285(6):4015-24
• Rapid-onset dystonia-parkinsonism in a child with a novel ATP1A3 gene mutation.
  Anselm IA, Sweadner KJ, Gollamudi S, Ozelius LJ, Darras BT.
  Neurology. 2009 Aug 4;73(5):400-1
• Multiplicity of expression of FXYD proteins in mammalian cells: dynamic exchange of phospholemman and gamma-subunit in response to stress.
  Arystarkhova E, Donnet C, Muñoz-Matta A, Specht SC, Sweadner KJ.
  Am J Physiol Cell Physiol. 2007 Mar;292(3):C1179-91
• Post-transcriptional control of Na,K-ATPase activity and cell growth by a splice variant of FXYD2 protein with modified mRNA.
  Sweadner KJ, Pascoa JL, Salazar CA, Arystarkhova E.
  J Biol Chem. 2011 May 20;286(20):18290-300
• FXYD proteins reverse inhibition of the Na+-K+ pump mediated by glutathionylation of its beta1 subunit.
  Bibert S, Liu CC, Figtree GA, Garcia A, Hamilton EJ, Marassi FM, Sweadner KJ, Cornelius F, Geering K, Rasmussen HH.
  J Biol Chem. 2011 May 27;286(21):18562-72

Dr. Kathleen J. Sweadner, PhD

Phone: 617-726-8579
Email: sweadner@helix.mgh.harvard.edu

Public Transportation Access: yes