Glanzmann thrombasthenia resulting from a single amino acid substitution between the second and third calcium-binding domains of GPIIb. Role of the GPIIb amino terminus in integrin subunit association.
To gain insight into region of the platelet GPIIb-IIIa complex involved in receptor biogenesis and function, we examined the biochemical properties of a defective GPIIb-IIIa complex from patient suffering from type II Glanzmann thrombasthenia. Flow cytometric as well as immunoblot analysis of patient platelets showed significantly reduced levels of GPIIb and GPIIIa compared with a normal control. Patient platelets, however, retained the ability to retract a fibrin clot. Sequence analysis of PCR-amplified platelet GPIIb mRNA revealed an Arg327-->His amino acid substitution between the second and third calcium-binding domains of the GPIIb heavy chain, a residue that is highly conserved among integrin alpha-subunits. The recombinant His327 form of GPIIb was found to be fully capable of associating with GPIIIa, therefore the role of the calcium-binding domains in intersubunit association was further examined by constructing amino-terminal segments of GPIIb that ended before the first, second, and third calcium-binding domains. All three fragments were found to associate with GPIIIa, demonstrating that the calcium-binding domains of GPIIb are not necessary for initial complex formation. Regions amino-terminal to the calcium-binding domains of GPIIb may play a heretofore unappreciated role in integrin subunit association.
Wilcox
D A
DA
Blood Research Institute, Blood Center of Southeastern Wisconsin, Milwaukee 53233, USA.
Paddock
C M
CM
Lyman
S
S
Gill
J C
JC
Newman
P J
PJ
D000293:Adolescent; D000595:Amino Acid Sequence; D001483:Base Sequence; D001792:Blood Platelets / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005340:Fibrinogen / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D016023:Integrins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010980:Platelet Membrane Glycoproteins / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D013329:Structure-Activity Relationship; D013915:Thrombasthenia / Q000235:genetics*
D016023:Integrins; D010980:Platelet Membrane Glycoproteins; D005340:Fibrinogen; D002118:Calcium