Summary
This work reports the structural and functional characterization of the platelet glycoprotein
complex GPIIb-IIIa (integrin αIIbβ3) in a patient of type II Glanzmann thrombasthenia, bearing a homozygous G→A base
transition at position 1074 of GPIIb that results in an Arg327→His substitution.
CHO cells stably transfected with cDNA encoding His327GPIIb showed a drastic reduction in the surface expression of αIIbβ3 complex relative to control cells transfected with wild type GPIIb. Immunopre-cipitation
analysis demonstrated that GPIIb synthesis, heterodimeriza-tion, and short term maturation
were not impeded, suggesting that conformational changes dependent on Arg327 of GPIIb may play an essential role in either the rate of maturation and/or transport
of heterodimers to the cell surface.
Cotransfection of CHO cells with equimolar amounts of cDNAs encoding wild type and
mutant His327-GPIIb led to a marked reduction in the surface expression of αIIbβ3. This novel observation of a dominant-negative effect of the mutant His327αIIb subunit provides a molecular basis for the reduced platelet αIIbβ3 content observed in the heterozygous offspring.