title: Small angle neutron scattering as sensitive tool to detect ligand-dependent shape changes in a plant lectin with beta-trefoil folding and their dependence on the nature of the solvent.
abstract: The galactoside-specific Viscum album L. agglutinin (VAA) is a potent biohazard akin to ricin and a mitogen for immune and tumor cells. These activities depend on cell surface binding to glycans. It is an open question whether the process of ligand binding alters the lectin's shape. Small angle neutron scattering (SANS) experiments revealed that the carbohydrate ligand lactose induced a decrease of the radius of gyration of dimeric VAA from 54.5 +/- 1 to 49.5 +/- 1 A in water. Apparently, VAA in aqueous solution and at the concentrations tested at 3.6 mg/ml and above adopts a compacted structure as response to ligand binding. In contrast to the behavior in aqueous solution, lactose binding in DMSO resulted in an increase of the lectin's radius of gyration from 49 +/- 1 to 55.5 +/- 1 A. Because shape changes may be reflected in the thermostability of the protein, this parameter was examined by activity assays of protein exposed to 60 degrees C and 70 degrees C and by differential scanning calorimetry (DSC). In line with the lactose-induced conformational alterations revealed by the SANS experiments, lactose presence enhanced the thermostability of VAA in water. Thus, binding of the carbohydrate ligand in solution can entail changes in shape and thermostability in the case of the tested plant lectin.
authors.affiliation: Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, QLD 4072, Australia. l.he@uq.edu.au
authors.forename: Lizhong
authors.initials: L
authors.lastname: He
authors.forename: Sabine
authors.initials: S
authors.lastname: André
authors.forename: Vasil M
authors.initials: VM
authors.lastname: Garamus
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Siebert
authors.forename: Chunyan
authors.initials: C
authors.lastname: Chi
authors.forename: Bernd
authors.initials: B
authors.lastname: Niemeyer
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Gabius
mesh_terms: D002152:Calorimetry, Differential Scanning / Q000379:methods; D004121:Dimethyl Sulfoxide / Q000737:chemistry* / Q000378:metabolism; D006358:Hot Temperature; D007785:Lactose / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D009502:Neutrons; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D054788:Ribosome Inactivating Proteins / Q000737:chemistry* / Q000378:metabolism; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological / Q000737:chemistry* / Q000378:metabolism; D028182:Viscum album / Q000737:chemistry*
chemical_list: D008024:Ligands; D011134:Polysaccharides; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C488865:VAA-I protein, Viscum album; D054788:Ribosome Inactivating Proteins; D007785:Lactose; D004121:Dimethyl Sulfoxide