Structure and function of platelet glycoprotein ib: Study of the functional domain of glycoprotein Ib for von Willebrand factor binding using granulocyte elastase-like proteinase.
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The structure of platelet glycoprotein Ib (GP Ib) and its functional domain for human von Willebrand factor (vWF) were investigated using an elastase-like proteinase (ELP) purified from human granulocytes and a monoclonal antibody (56-2) against GP Ib which completely inhibited the interaction of platelets with human vWF. Treatment of platelets with ELP resulted in loss of their ability to interact with human vWF in the presence of ristocetin. A fluorogram of SDS-PAGE of 3H-labelled platelets treated with ELP revealed that a band corresponding to GP Ib was clearly decreased and fragments with molecular weights (MW) of 97 kilo-daltons (KD), 70 KD, 60, KD, 47 KD, 44 KD, 37 KD, 25 KD and 15 KD were released from the platelets. The 47 KD fragment was initially cleaved from the platelets, and the 25 KD fragment showed a much fainter band when compared with the 47 KD and 44 KD fragments. Similar results were obtained when partially purified GP Ib was digested by ELP. When these fragments were reacted with 56-2 antibody, the fragments with MW of 47 KD, 44 KD and 25 KD were immunoisolated. The electrophoretic mobility of these three bands was slightly slow under reduced conditions compared with the results obtained under non-reduced conditions. The fragment of MW 25 KD should be derived from the fragments with MW of 47 KD and 44 KD, since these three fragments have an epitope to 56-2 antibody. The results obtained suggest that the functional domain of GP Ib for human vWF binding may be located in a less glycosylated fragment of MW 25 KD on the distal portion of GP Ib, which should contain loop region with at least one intramolecular disulfide bond, and this region may be important for the interaction of platelets with human vWF.
- The Keio Journal of Medicineの論文