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Glycoprotein Ibalpha forms disulfide bonds with 2 glycoprotein Ibbeta subunits in the resting platelet

Shi-Zhong Luo1, Xi Mo, Vahid Afshar-Kharghan

  • 1Center for Membrane Biology, Department of Biochemistry and Molecular Biology, The University of Texas Health Science Center at Houston, MSB 6.130, 6431 Fannin St, Houston, TX 77030, USA.

Blood
|September 30, 2006
PubMed

Insights

Glycoprotein Ib (GP Ib) has an Ibalpha subunit linked to two Ibbeta subunits via disulfide bonds, not one. This finding revises the structure of the GP Ib-IX-V complex in platelets.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Background:

  • The glycoprotein Ib (GP Ib) complex is crucial for platelet adhesion and aggregation.
  • The precise subunit stoichiometry and disulfide bonding within GP Ib remain incompletely understood.

Purpose of the Study:

  • To elucidate the specific cysteine residues involved in the disulfide bond between Ibalpha and Ibbeta subunits.
  • To determine the stoichiometry of subunits within the GP Ib-IX complex.

Main Methods:

  • Site-directed mutagenesis of cysteine residues in Ibalpha and Ibbeta subunits.
  • Co-immunoprecipitation assays to analyze subunit interactions.
  • Analysis of GP Ib from transfected cells and human platelets.

Main Results:

  • Both C484 and C485 in Ibalpha form disulfide bonds with C122 in Ibbeta.
  • The GP Ib-IX complex contains at least two Ibbeta subunits for every one Ibalpha and one IX subunit.
  • Observed size differences in GP Ib are due to sequence and glycosylation variations in Ibalpha.

Conclusions:

  • The resting platelet GP Ib complex exhibits an Ibalpha(2)Ibbeta(2) composition, challenging previous models.
  • This revised stoichiometry necessitates a re-evaluation of the GP Ib-IX-V complex structure.
  • The alphabeta2 composition suggests potential for disulfide bond rearrangements within the receptor.

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