The 33-kDa platelet alpha-granule membrane protein (GMP-33) is an N-terminal proteolytic fragment of thrombospondin.
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 alpha-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.
Damas
C
C
Department of Haematology and Graduate School for Biomembranes, University of Utrecht, The Netherlands.
Vink
T
T
Nieuwenhuis
H K
HK
Sixma
J J
JJ
D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D001792:Blood Platelets / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry*; D003429:Cross Reactions; D003594:Cytoplasmic Granules / Q000737:chemistry*; D010450:Endopeptidases / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006031:Glycosylation; D006493:Heparin / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry*; D008565:Membrane Proteins; D010446:Peptide Fragments / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D019699:Thrombospondins / Q000737:chemistry* / Q000187:drug effects / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism
D000911:Antibodies, Monoclonal; C451331:GMP-33 protein, human; D008565:Membrane Proteins; D010446:Peptide Fragments; D019699:Thrombospondins; D006493:Heparin; D010450:Endopeptidases