C-terminal amino acid determination of the transmembrane subunits of the human platelet fibrinogen receptor, the GPIIb/IIIa complex.
Glycoproteins IIb (GPIIb) and IIIa (GPIIIa) form the Ca2(+)-dependent GPIIb/IIIa complex, which acts as the fibrinogen receptor on activated platelets. GPIIb and GPIIIa are synthesized as single peptide chains. The GPIIb precursor is processed proteolytically to yield two disulphide-bonded chains, GPIIb alpha and GPIIb beta. The GPIIb/IIIa complex has two membrane attachment sites located at the C-termini of GPIIb beta and GPIIIa. The short cytoplasmic tails of GPIIb beta and/or GPIIIa become most likely associated to the cytoskeleton of activated platelets. In the present work the C-terminal amino acid residues of platelet GPIIb beta and GPIIIa have been analyzed by protein-chemical methods and compared with those predicted from cDNA analysis. We were able to confirm the positions of the C-termini in both glycoproteins and the identity of the C-terminus predicted for GPIIIa, i.e. threonine. However, glutamine, not glutamic acid as predicted for GPIIb beta from the human erythroleukemic cell line and megakaryocyte cells, was found to be the C-terminal amino acid of GPIIb beta. This indicates that the glutamic acid in the GPIIb precursor is posttranslationally modified to glutamine.
Calvete
J J
JJ
Max-Planck-Institut für Biochemie, Martinsried, FRG.
Schäfer
W
W
Henschen
A
A
Gonzalez-Rodriquez
J
J
D000595:Amino Acid Sequence; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification; D010449:Peptide Mapping; D010980:Platelet Membrane Glycoproteins / Q000235:genetics* / Q000302:isolation & purification; D014357:Trypsin
D046911:Macromolecular Substances; D010446:Peptide Fragments; D010980:Platelet Membrane Glycoproteins; D014357:Trypsin