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Multiple interactions of HIV-I Tat protein with size-defined heparin oligosaccharides
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology.
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1999 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 274, no 40, 28198-28205 p.Article in journal (Refereed) Published
Abstract [en]

Tat protein, a transactivating factor of the human immunodeficiency virus type I, acts also as an extracellular molecule. Heparin affects the bioavailability and biological activity of extracellular Tat (Rusnati, M., Coltrini, D., Oreste, P., Zoppetti, G., Albini, A., Noonan, D., D'Adda di Fagagna, F., Giacca, M., and Presta, M. (1997) J. Biol. Chem. 272, 11313-11320). Here, a series of homogeneously sized, (3)H-labeled heparin fragments were evaluated for their capacity to bind to free glutathione S-transferase (GST)-Tat protein and to immobilized GST-Tat. Hexasaccharides represent the minimum sized heparin fragments able to interact with GST-Tat at physiological ionic strength. Also, the affinity of binding increases with increasing the molecular size of the oligosaccharides, with large fragments (>/=18 saccharides) approaching the affinity of full-size heparin. 6-Mer heparin binds GST-Tat with a dissociation constant (K(d)) equal to 0.7 +/- 0.4 microM and a molar oligosaccharide:GST-Tat ratio of about 1:1. Interaction of GST-Tat with 22-mer or full-size heparin is consistent instead with two-component binding. At subsaturating concentrations, a single molecule of heparin interacts with 4-6 molecules of GST-Tat with high affinity (K(d) values in the nanomolar range of concentration); at saturating concentrations, heparin binds GST-Tat with lower affinity (K(d) values in the micromolar range of concentration) and a molar oligosaccharide:GST-Tat ratio of about 1:1. In agreement with the binding data, a positive correlation exists between the size of heparin oligosaccharides and their capacity to inhibit cell internalization, long terminal repeat-transactivating activity of extracellular Tat in HL3T1 cells, and its mitogenic activity in murine adenocarcinoma T53 Tat-less cells. The data demonstrate that the modality of heparin-Tat interaction is strongly affected by the size of the saccharide chain. The possibility of establishing multiple interactions increases the affinity of large heparin fragments for Tat protein and the capacity of the glycosaminoglycan to modulate the biological activity of extracellular Tat.

Place, publisher, year, edition, pages
1999. Vol. 274, no 40, 28198-28205 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:uu:diva-155975DOI: 10.1074/jbc.274.40.28198PubMedID: 10497173OAI: oai:DiVA.org:uu-155975DiVA: diva2:429521
Available from: 2011-07-04 Created: 2011-07-04 Last updated: 2011-07-08Bibliographically approved

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Spillmann, Dorothe
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