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Alterations in the α2 isoform of Na,K-ATPase associated with familial hemiplegic migraine type 2

  1. Laura Segall †,
  2. Alessandra Mezzetti ‡,
  3. Rosemarie Scanzano †,
  4. J. Jay Gargus §,
  5. Enrico Purisima ‡, and
  6. Rhoda Blostein † ,
  1. †Departments of Biochemistry and Medicine, McGill University and Montreal General Hospital Research Institute, Montreal, QC, Canada H3G 1A4; ‡Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, QC, Canada H4P 2R2; and §Departments of Physiology and Biophysics and Pediatrics, Section of Human Genetics, University of California, Irvine, CA 92697-4034

  1. Communicated by Joseph F. Hoffman, Yale University School of Medicine, New Haven, CT, May 25, 2005 (received for review March 16, 2005)

Abstract

A number of missense mutations in the Na,K-ATPase α2 catalytic subunit have been identified in familial hemiplegic migraine with aura. Two alleles (L764P and W887R) showed loss-of-function, whereas a third (T345A) is fully functional but with altered Na,K-ATPase kinetics. This study describes two additional mutants, R689Q and M731T, originally identified by Vanmolkot et al. [Vanmolkot, K. R., et al. (2003) Ann. Neurol. 54, 360-366], which we show here to also be functional and kinetically altered. Both mutants have reduced catalytic turnover and increased apparent affinity for extracellular K+. For both R689Q and M731T, sensitivity to vanadate inhibition is decreased, suggesting that the steady-state E1 ↔ E2 poise of the enzyme is shifted toward E1. Whereas the K′ATP is not affected by the R689Q replacement, the M731T mutant has an increase in apparent affinity for ATP. Analysis of the structural changes effected by T345A, R689Q, and M731T mutations, based on homologous replacements in the known crystal structure of the sarcoplasmic reticulum Ca-ATPase, provides insights into the molecular bases for the kinetic alterations. It is suggested that the disease phenotype is the consequence of lowered molecular activity of the α2 pump isoform due to either decreased K+ affinity (T345A) or catalytic turnover (R689Q and M731T), thus causing a delay in extracellular K+ clearance and/or altered localized Ca2+ handling/signaling secondary to reduced activity in colocalized Na+/Ca2+ exchange.

Footnotes

  • ↵ To whom correspondence should be addressed. E-mail: rhoda.blostein{at}mcgill.ca.

  • Author contributions: L.S. and R.B. designed research; L.S. and R.S. performed research; A.M. and E.P. contributed new reagents/analytic tools; A.M., R.S., and E.P. analyzed data; and L.S., J.J.G., and R.B. wrote the paper.

  • Abbreviation: FHM, familial hemiplegic migraine.

  • ↵ ∥ α2* denotes the relatively ouabain-insensitive rat α2 enzyme (14).

  • ↵ †† Residues in italics refer to residues in SERCA homologous to those in the Na, K-ATPase α2.

  • Freely available online through the PNAS open access option.

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