Thromb Haemost 2001; 86(03): 887-893
DOI: 10.1055/s-0037-1616152
Review Articles
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The 33-kDa Platelet α-granule Membrane Protein (GMP-33) Is an N-terminal Proteolytic Fragment of Thrombospondin

Conchi Damas
1   Department of Haematology and Graduate School for Biomembranes, University of Utrecht, The Netherlands
,
Tom Vink
1   Department of Haematology and Graduate School for Biomembranes, University of Utrecht, The Netherlands
,
Karel H. Nieuwenhuis
1   Department of Haematology and Graduate School for Biomembranes, University of Utrecht, The Netherlands
,
Jan J. Sixma
1   Department of Haematology and Graduate School for Biomembranes, University of Utrecht, The Netherlands
› Author Affiliations

This work was financially supported by the Dutch Heart Foundation (NHS) (grant no. 43.051).
Further Information

Publication History

Received 12 December 2000

Accepted after revision 07 May 2001

Publication Date:
14 December 2017 (online)

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Summary

GMP-33 is a platelet membrane associated protein that is recognised by RUU-SP 1.77, an antibody raised against activated platelets. GMP-33 is predominantly associated with the membrane of platelet α-granules and it is translocated to the plasma membrane upon platelet activation (Metzelaar et al. Blood 1992; 79: 372-9). In this study we have isolated the protein by immunoaffinity chromatography. The N-terminus was sequenced and was identical to the N-terminal sequence of human thrombospondin. The protein was N-glycosylated and bound to heparin as would be expected of the N-terminal part of thrombospondin. RUU-SP 1.77 reacted only with reduced thrombospondin. Plasmin and trypsin digestion of thrombospondin yielded fragments of approximately the same size as GMP 33 that reacted with RUU-SP 1.77 after reduction. No evidence for alternative splicing was found. We postulate that GMP 33 is an N-terminal proteolytic fragment of thrombospondin that is membrane associated.