Distinction between glycoprotein IIIa and the 100-kDa membrane protein (aggregin) mediating ADP-induced platelet activation.
Previous studies from our laboratories showed that 5'-p-fluorosulfonylbenzoyl adenosine (FSBA) inhibits ADP-induced platelet shape change, aggregation, and exposure of fibrinogen sites while covalently binding to 100-kDa platelet membrane protein (aggregin) on the intact platelet. Chymotrypsin digests aggregin to a fragment of 70 kDa, abolishing the inhibition, and also cleaves platelet glycoprotein IIIa (GPIIIa) (100 kDa) to a 70-kDa fragment containing the P1A1 epitope. We questioned whether these platelet membrane proteins were distinct. Both 5'-p-[3H]sulfonylbenzoyl adenosine (SBA)-labeled aggregin and 125I-GPIIIa were precipitated by polyclonal antibodies to a 100-kDa fraction of platelet membranes, but aggregin was not precipitated by a monospecific antibody to P1A1 which precipitates GPIIIa. Further a monospecific polyclonal antibody to immunopurified GPIIIa coupled to protein A-Sepharose adsorbed GPIIIa but not aggregin. Similarly, both aggregin and GPIIIa were precipitated by a polyclonal antibody to an isolated 70-kDa component of platelet membrane but only GPIIIa was precipitated by the monoclonal antibody to GPIIIa, (SSA6). Two patients with Glanzman's thrombasthenia whose platelet membranes contained less than 5% GPIIIa as assayed by monoclonal antibody binding (A2A6), incorporated [3H]SBA to the same extent as normal individuals. Furthermore, FSBA inhibited ADP-induced shape change with a similar concentration dependence for both thrombasthenic and normal platelets. Finally, mobility of GPIIIa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was decreased following reduction with dithiothreitol whereas that of [3H]SBA-labeled MP 100 was not altered. We conclude that GPIIIa and aggregin are distinct platelet membrane proteins.
Colman
R W
RW
Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
Figures
W R
WR
Wu
Q X
QX
Chung
S Y
SY
Morinelli
T A
TA
Tuszynski
G P
GP
Colman
R F
RF
Niewiarowski
S
S
D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007163:Immunosorbent Techniques; D008970:Molecular Weight; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000032:analysis*; D011817:Rabbits; D011983:Receptors, Purinergic / Q000032:analysis*
D010980:Platelet Membrane Glycoproteins; D011983:Receptors, Purinergic; C055422:aggregin; D000244:Adenosine Diphosphate; C010959:5'-(4-fluorosulfonylbenzoyl)adenosine; D000241:Adenosine