title: Different affinity of galectins for human serum glycoproteins: galectin-3 binds many protease inhibitors and acute phase proteins.
abstract: Here we report the first survey of galectins binding to glycoproteins of human serum. Serum was subjected to affinity chromatography using immobilized galectins, and the bound glycoproteins were analyzed by electrophoresis, Western blotting, and mass spectrometry. Galectins-3, -8, and -9 bound a much broader range of ligands in serum than previously known, galectin-1 bound less, and galectins-2, -4, and -7 bound only traces or no serum ligands. Galectin-3 bound most major glycoproteins, including alpha-2-macroglobulin and acute phase proteins such as haptoglobin. It bound only a selected minor fraction of transferrin, and bound none or little of IgG. Galectins-8 and -9 bound a similar range of glycoproteins as galectin-3, but in lower amounts, and galectin-8 had a relative preference for IgA. Galectin-1 bound mainly a fraction of alpha-2-macroglobulin and only traces of other glycoproteins. The binding of galectin-3 to serum glycoproteins requires affinity for LacNAc, since a mutant (R186S), which has lost this affinity, did not bind any serum glycoproteins. The average affinity of galectin-3 for serum glycoproteins was estimated to correspond to K(d) approximately 1-5 muM by modeling of the affinity chromatography and a fluorescence anisotropy assay. Since galectins are expressed on endothelial cells and other cells exposed to serum components, this report gives new insight into function of galectins and the role of their different fine specificity giving differential binding to the serum glycoproteins.
authors.affiliation: Department of Laboratory Medicine, Section MIG (Microbiology, Immunology, Glycobiology), Lund University, 223-62 Lund, Sweden. cecilia.cederfur@med.lu.se
authors.forename: Cecilia
authors.initials: C
authors.lastname: Cederfur
authors.forename: Emma
authors.initials: E
authors.lastname: Salomonsson
authors.forename: Jonas
authors.initials: J
authors.lastname: Nilsson
authors.forename: Adnan
authors.initials: A
authors.lastname: Halim
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Oberg
authors.forename: Göran
authors.initials: G
authors.lastname: Larson
authors.forename: Ulf J
authors.initials: UJ
authors.lastname: Nilsson
authors.forename: Hakon
authors.initials: H
authors.lastname: Leffler
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism*; D001665:Binding Sites; D002846:Chromatography, Affinity; D005454:Fluorescence Polarization; D037502:Galectin 3 / Q000378:metabolism*; D037161:Galectins / Q000378:metabolism*; D006023:Glycoproteins / Q000097:blood* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D011480:Protease Inhibitors / Q000378:metabolism*
chemical_list: D000209:Acute-Phase Proteins; D037502:Galectin 3; D037161:Galectins; D006023:Glycoproteins; C091991:LGALS8 protein, human; C105032:LGALS9 protein, human; D008024:Ligands; D011480:Protease Inhibitors