Glycobiology Advance Access originally published online on November 3, 2005
Glycobiology 2006 16(3):173-183; doi:10.1093/glycob/cwj053
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2,6-Sialylation promotes binding of placental protein 14 via its Ca2+-dependent lectin activity: insights into differential effects on CD45RO and CD45RA T cells
2 Goldyne Savad Institute of Gene Therapy, Hadassah-Hebrew University Medical Center, Jerusalem, Israel; 3 Glycominds Ltd., Lod 71291, Israel; 4 Institute of Physiological Chemistry, Ludwig-Maximilians-University, Veterinärstraße 13, D-80539 Munich, Germany; and 5 Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104
1 To whom correspondence should be addressed; e-mail: rjacob{at}md.huji.ac.il
Received on July 28, 2005; revised on October 2, 2005; accepted on October 27, 2005
Placental protein 14 (PP14; glycodelin) is a pregnancy-associated immunoregulatory protein that is known to inhibit T cells via T-cell receptor desensitization. The recent demonstration of PP14 as lectin has provided insight into how it may mediate its CD45 glycoprotein-dependent T-cell inhibition. In this study, we have investigated PP14’s lectin-binding properties in detail. Significantly, PP14 reacts with N-acetyllactosamine (LacNAc) as was also found for members of the galectin family, such as the potent immunoregulatory protein, galectin-1. However, in contrast to galectin-1, PP14’s binding is significantly enhanced by 
2,6-sialylation and also by the presence of cations. This was demonstrated by preferential binding to fetuin as compared with its desialylated variant asialofetuin (ASF) and by using free 2,6- versus 2,3-sialylated forms of LacNAc in competitive inhibition and direct solid-phase binding assays. Interestingly, from immunological point of view, PP14 also binds differentially to CD45 isoforms known to differ in their degree of sialylation. PP14 preferentially inhibits CD45RA+, as compared with CD45RO+ T cells, and preferentially co-capped this variant CD45 on the T-cell surface. Finally, we demonstrate that PP14 promotes CD45 dimerization and clustering, a phenomenon that may regulate CD45 activity.
Key words: CD45 / galectin / glycodelin / sialic acid / T cell
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