title: Organization of human interferon gamma-heparin complexes from solution properties and hydrodynamics.
abstract: Heparan sulfate (HS) recognizes a variety of proteins, one of which is the pleiotropic cytokine IFN-gamma, and as such modulates many biological processes. IFN-gamma is a homodimer with a well-defined core and two flexible C-termini that constitute HS binding domains. We show here using molecular modeling that an extended IFN-gamma structure overlaps a HS fragment of 16 disaccharides (16 nm). Since a 21-24-disaccharide HS fragment was experimentally defined as the minimum size that interacts with IFN-gamma [Lortat-Jacob, H., Turnbull, J. E., and Grimaud, J. A. (1995) Biochem. J. 310 (Part 2), 497-505], this raises the question of the complexe organization. We combine analytical ultracentrifugation, size exclusion chromatography, and hydrodynamic bead modeling to characterize the complexes formed in solution with heparin oligosaccharides. For oligosaccharides of 14 and 20 nm, two types of complexes are formed with one IFN-gamma and one or two heparin molecules. Complexes consisting of two IFN-gamma and one or two heparin molecules are present for a fragment of 25 nm and aggregates for a fragment of 35 nm. The complexes are rather compact and can be formed without major conformational changes of the partners. The complex pattern of interaction is related to the size of the partners and their multiple binding possibilities. These various possibilities suggest networks of interactions at the crowded surface of the cells. Hydrodynamic methods used here proved to be very efficient tools for describing protein-HS complexes that, due to the intrinsic heterogeneity and flexibility of the partners, are otherwise very difficult to analyze.
authors.affiliation: Departamento de Quimica Fisica, Universidad de Murcia, 30071 Murcia, Spain.
authors.forename: Horacio
authors.initials: H
authors.lastname: Perez Sanchez
authors.forename: Karine
authors.initials: K
authors.lastname: Tatarenko
authors.forename: Michael
authors.initials: M
authors.lastname: Nigen
authors.forename: Georges
authors.initials: G
authors.lastname: Pavlov
authors.forename: Anne
authors.initials: A
authors.lastname: Imberty
authors.forename: Hugues
authors.initials: H
authors.lastname: Lortat-Jacob
authors.forename: Jose
authors.initials: J
authors.lastname: Garcia de la Torre
authors.forename: Christine
authors.initials: C
authors.lastname: Ebel
mesh_terms: D002850:Chromatography, Gel; D006493:Heparin / Q000737:chemistry*; D007371:Interferon-gamma / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D012996:Solutions; D014461:Ultracentrifugation
chemical_list: D012996:Solutions; D007371:Interferon-gamma; D006493:Heparin