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Poster Sessions| November 16, 2004

An Externally Active Endogenous Platelet Galactosyl Trasferase (Gal-T).

Karin M. Hoffmeister,

Karin M. Hoffmeister

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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Hans H. Wandall,

Hans H. Wandall *

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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Vasanthi Sankaranarayanan,

Vasanthi Sankaranarayanan *

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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Henrik Clausen,

Henrik Clausen *

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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Thomas P. Stossel,

Thomas P. Stossel

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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John H. Hartwig

John H. Hartwig

¹Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA ; ²School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ³School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁴School of Dentistry, University of Copenhagen, Copenhagen, Denmark ; ⁵Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA and ⁶Division of Hematology, Brigham and Women’s Hospital, Boston, MA, USA.

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Blood (2004) 104 (11): 3525.

https://doi.org/10.1182/blood.V104.11.3525.3525

Abstract

Over 30 years ago, Jamison and Barber proposed that externally disposed glycosyl transferase (GT) activity mediates platelet adhesion and other functions. Subsequent work ruled out ecto-GT activity in nucleated cells and established the Golgi as the site of such enzymes, although no further studies examined platelets. We recently reported a platelet-associated galactosyl transferase (β4Gal-T) catalyzing galactose coupling in a β1,4 linkage to exposed N-acetylglucosamine (GlcNAc) residues on N-linked glycans of the GPIbα subunit of the von Willebrand factor receptor complex. This activity, also present in plasma, mediates galactose transfer to GPIbα following addition of UDP-galactose (UDP-Gal) alone. Since galactosylation of GPIbα prevents clearance of chilled platelets by liver macrophages after transfusion, sufficiently active endogenous endogenous β4Gal-T could facilitate platelet cold storage after the mere addition of substrate UDP-Gal (

Science 301: 1531–1534, 2003

). We now give evidence that human platelets contain a highly active (0.05 nmol/min) plasma membrane-associated ecto-β4Gal-T with properties of an isoform designated as type 1 (β4Gal-T1). A specific β4Gal-T1 antibody immunoprecipitates β4Gal-T1 activity from platelet lysates and the inhibition profile activity by α-lactalbumin and benzyl-β-D-GlcNAc are characteristic of β4Gal-T1. β4Gal-T1 has a transmembrane domain, and platelet β4Gal-T, although releasable by non-ionic detergent, remains cell- and membrane associated despite extensive washing. The platelet enzyme incorporates UDP-[C14]Gal into a single polypeptide with the apparent Mr of GPIbα, identifying this protein as its unique endogenous target. Nevertheless, washed platelets are as active as recombinant β4Gal-T1 in galactosylating exogenous substrates, benzyl-β-D-GlcNAc and ovalbumin. In conclusion, we have revived the concept of an ecto-glycosyl transferase on blood platelets and demonstrated that platelet β4Gal-T is probably sufficiently active to accommodate reliable enzymatic conversion of platelets by simple addition of UDP-Gal.

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2005, The American Society of Hematology

2004

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