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Role of the transmembrane domain of glycoprotein IX in assembly of the glycoprotein Ib–IX complex
Author(s) -
LUO S.Z.,
MO X.,
LÓPEZ J. A.,
LI R.
Publication year - 2007
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2007.02785.x
Subject(s) - platelet glycoprotein gpib ix complex , glycoprotein , cytoplasm , chinese hamster ovary cell , microbiology and biotechnology , platelet membrane glycoprotein , chemistry , von willebrand factor , transmembrane domain , biology , biochemistry , amino acid , platelet , receptor , immunology
Summary. Background: The glycoprotein (GP) Ib–IX complex is critically involved in platelet adhesion to von Willebrand factor and in the initial step of platelet activation. How this complex is assembled is not clear. We previously showed that the transmembrane (TM) domains of the GPIbα and GPIbβ subunits interact and participate in complex assembly. Objectives and methods: Here, we have investigated the role of the TM and cytoplasmic domains of GPIX in assembly of the GPIb–IX complex, by analyzing the mutational effects on complex expression and assembly in transiently transfected Chinese hamster ovary cells. Results: Replacing the cytoplasmic domain of GPIX with a poly‐alanine sequence had little effect on surface expression and structural integrity of the GPIb–IX complex. In contrast, replacing the GPIX TM domain (residues 132–153) with a poly‐leucine‐alanine sequence markedly disrupted complex formation of GPIX with GPIbα, interfered with GPIb formation, and decreased surface expression of the host complex. We further analyzed the contributions of a number of GPIX TM residues to complex formation by mutagenesis and found significant roles for Asp135 and several Leu residues. Conclusions: The TM domain, rather than the cytoplasmic domain, of GPIX plays an important role in expression and assembly of the GPIb–IX complex by interacting with its counterparts of GPIb. These TM domains may form a parallel four‐helical bundle structure in the complex.