Characterization of a novel self-associating Mr 40,000 platelet
glycoprotein [see comments]
JE Hildreth, D Derr and DO Azorsa
Department of Pharmacology and Molecular Sciences, Johns Hopkins
University, School of Medicine, Baltimore, MD 21205.
A novel platelet glycoprotein has been purified and characterized. This
glycoprotein, designated Pltgp40, is an acidic sialylated 40,000-dalton
protein that bears both O-linked and N-linked oligosaccharides. Treatment
of Pltgp40 with neuraminidase resulted in a 5,000-dalton reduction in its
Mr and a 1.5 Unit alkaline shift in the isoelectric point, indicating the
presence of a large number of sialic acid residues. A similar size
reduction and change in pl were observed after treatment of Pltgp40 with
O-glycanase showing that sialic acids are present on O-linked
oligosaccharides. Digestion of Pltgp40 with N- glycanase reduced the Mr to
approximately 20,000 daltons but did not affect the isoelectric point,
suggesting that Pltgp40 contains six to seven nonsialylated N-linked
carbohydrate chains. High Mr proteins were observed in affinity purified
Pltgp40 and were identified as detergent- stable protein oligomers
consisting of multiple 40,000-dalton monomers. Immunodepletion and direct
binding studies indicated that Pltgp40 was not equivalent to Ig Fc receptor
type II, another 40,000-dalton glycoprotein expressed on platelets.
However, Pltgp40 copurified with Fc receptor type II when platelet extracts
were loaded onto human IgG affinity columns, raising the possibility that
Pltgp40 may associate with Fc receptors or Fc receptor-lg complexes. Amino
acid sequence analysis of the N-terminus of Pltgp40 was performed and
confirmed that Pltgp40 is a novel platelet glycoprotein. Epitopes on
Pltgp40 appear to be widely expressed because monoclonal antibodies against
Pltgp40 also reacted with a variety of myeloid, lymphoid, and epithelial
cells. Pltgp40 was detected on activated but not resting platelets,
indicating that Pltgp40 is a platelet activation marker.
Volume 77,
Issue 1,
pp. 121-132,
01/01/1991
Copyright © 1991 by The American Society of Hematology
