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Effect of single amino acid substitutions on the formation of the PlA and
Bak alloantigenic epitopes
A Goldberger, M Kolodziej, M Poncz, JS Bennett and PJ Newman
Blood Center of Southeastern Wisconsin, Milwaukee 53233.
The subunits that comprise the platelet-specific integrin alpha IIb beta 3
are polymorphic in nature, with several allelic forms present in the human
gene pool. Minor changes in the secondary and tertiary structures of
platelet membrane glycoproteins (GP) IIb and IIIa encoded by these alleles
can result in an alloimmune reaction after transfusion or during pregnancy.
To better understand the molecular structure of the PlA alloantigen system,
located on GPIIIa, and the Bak alloantigen on GPIIb, we used a heterologous
mammalian expression system to express these integrin subunits in their
known polymorphic forms. An expression vector containing the PlA1 form of a
GPIIIa cDNA, which encodes a leucine at amino acid 33 (Leu33), was modified
to express the PlA2- associated form encoding a proline at amino acid 33
(Pro33). Similarly, a Baka GPIIb cDNA expressing an isoleucine at amino
acid 843 (IIe843) was modified to express the Bakb form containing a serine
at the same position (Ser843). Transfection of these vectors into COS cells
resulted in the synthesis of GPIIb and GPIIIa molecules that were identical
in size to those present in platelet lysates. Immunoprecipitation of the
GPIIIa-transfected COS lysates with PlA)- specific alloantisera indicated
that the Leu33 form was recognized only by anti-PIA1 sera while the Pro33
form was bound only by anti-PlA2 sera, showing that single amino acid
polymorphisms are necessary and sufficient to direct the formation of the
PlA1 and PlA2 alloepitopes. Similar experiments with Bak allele-specific
expression vectors indicated that while the amino acid polymorphism (IIe843
in equilibrium Ser843) was necessary, posttranslational processing of
pro-IIb was required for efficient exposure of both the Baka and Bakb
alloepitopes.
Volume 78,
Issue 3,
pp. 681-687,
08/01/1991
Copyright © 1991 by The American Society of Hematology
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