An αIIb mutation in patients with Glanzmann thrombasthenia located in the N-terminus of blade 1 of the β-propeller (Asn2Asp) disrupts a calcium binding site in blade 6

W. Mansour, Y. Einav, H. Hauschner, A. Koren, U. Seligsohn*, N. Rosenberg

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Background: Studies of Glanzmann thrombasthenia (GT)-causing mutations has generated invaluable information on the formation and function of integrin αIIbβ3. Objective: To characterize the mutation in four siblings of an Israeli Arab family affected by GT, and to analyze the relationships between the mutant protein structure and its function using artificial mutations. Methods and Results: Sequencing disclosed a new A97G transversion in the αIIb gene predicting Asn2Asp substitution at blade 1 of the β-propeller. Alignment with other integrin α subunits revealed that Asn2 is highly conserved. No surface expression of αIIbβ3 was found in patients' platelets and baby hamster kidney (BHK) cells transfected with mutated αIIb and WT β3. Although the αIIbβ3 was formed, the mutation impaired its intracellular trafficking. Molecular dynamics simulations and modeling of the αIIbβ3 crystal indicated that the Asn2Asp mutation disrupts a hydrogen bond between Asn2 and Leu366 of a calcium binding domain in blade 6, thereby impairing calcium binding that is essential for intracellular trafficking of αIIbβ3. Substitution of Asn2 to uncharged Ala or Gln partially decreased αIIbβ3 surface expression, while substitution by negatively or positively charged residues completely abolished surface expression. Unlike αIIbβ3, αVβ3 harboring the Asn2Asp mutation was surface expressed by transfected BHK cells, which is consistent with the known lower sensitivity of αVβ3 to calcium chelation compared with αIIbβ3. Conclusion: The new GT causing mutation highlights the importance of calcium binding domains in the β-propeller for intracellular trafficking of αIIbβ3. The mechanism by which the mutation exerts its deleterious effect was elucidated by molecular dynamics.

Original languageEnglish
Pages (from-to)192-200
Number of pages9
JournalJournal of Thrombosis and Haemostasis
Volume9
Issue number1
DOIs
StatePublished - Jan 2011

Keywords

  • Glanzmann thrombasthenia
  • Integrins
  • Molecular dynamics
  • αIIb mutations
  • β-propeller

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