title: Ligand reduces galectin-1 sensitivity to oxidative inactivation by enhancing dimer formation.
abstract: Galectin-1 (Gal-1) regulates leukocyte turnover by inducing the cell surface exposure of phosphatidylserine (PS), a ligand that targets cells for phagocytic removal, in the absence of apoptosis. Gal-1 monomer-dimer equilibrium appears to modulate Gal-1-induced PS exposure, although the mechanism underlying this regulation remains unclear. Here we show that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidation. A mutant form of Gal-1, containing C2S and V5D mutations (mGal-1), exhibits impaired dimerization and fails to induce cell surface PS exposure while retaining the ability to recognize carbohydrates and signal Ca(2+) flux in leukocytes. mGal-1 also displayed enhanced sensitivity to oxidation, whereas ligand, which partially protected Gal-1 from oxidation, enhanced Gal-1 dimerization. Continual incubation of leukocytes with Gal-1 resulted in gradual oxidative inactivation with concomitant loss of cell surface PS, whereas rapid oxidation prevented mGal-1 from inducing PS exposure. Stabilization of Gal-1 or mGal-1 with iodoacetamide fully protected Gal-1 and mGal-1 from oxidation. Alkylation-induced stabilization allowed Gal-1 to signal sustained PS exposure in leukocytes and mGal-1 to signal both Ca(2+) flux and PS exposure. Taken together, these results demonstrate that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidative inactivation and provides a mechanism whereby ligand partially protects Gal-1 from oxidation.
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Stowell
authors.forename: Moonjae
authors.initials: M
authors.lastname: Cho
authors.forename: Christa L
authors.initials: CL
authors.lastname: Feasley
authors.forename: Connie M
authors.initials: CM
authors.lastname: Arthur
authors.forename: Xuezheng
authors.initials: X
authors.lastname: Song
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Colucci
authors.forename: Sougata
authors.initials: S
authors.lastname: Karmakar
authors.forename: Padmaja
authors.initials: P
authors.lastname: Mehta
authors.forename: Marcelo
authors.initials: M
authors.lastname: Dias-Baruffi
authors.forename: Rodger P
authors.initials: RP
authors.lastname: McEver
authors.forename: Richard D
authors.initials: RD
authors.lastname: Cummings
mesh_terms: D000478:Alkylation / Q000187:drug effects; D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D019281:Dimerization; D037483:Galectin 1 / Q000235:genetics / Q000378:metabolism*; D018922:HL-60 Cells; D006801:Humans; D007460:Iodoacetamide / Q000494:pharmacology; D007962:Leukocytes / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D020125:Mutation, Missense; D010084:Oxidation-Reduction / Q000187:drug effects; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology*; D010718:Phosphatidylserines / Q000378:metabolism* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
chemical_list: D037483:Galectin 1; D008024:Ligands; D010718:Phosphatidylserines; D002118:Calcium; D007460:Iodoacetamide