title: Probing the nature of the cluster effect observed with synthetic multivalent galactosides and peanut agglutinin lectin.
abstract: We designed a set of multi-galactosides with valencies ranging from one to seven and different spacer-arm lengths. The compounds display a high structural homology for a strict assessment of multivalent phenomena. The multimers were first evaluated by an enzyme-linked lectin assay (ELLA) toward the peanut agglutinin (PNA). The binding affinity was shown to be dependent on the spacer-arm length, and cluster effects were observed for the galactosides bearing the shortest and the longest linkers. The latter compounds were shown to be much more potent PNA cross-linkers in a "sandwich assay". Dynamic light scattering (DLS) experiments also revealed the formation of soluble aggregates between heptavalent derivatives with medium or long linkers and the labeled PNA. ELLA experiments performed with valency-controlled clusters and labeled lectins are therefore not always devoid from aggregative processes. The precise nature of the multivalent interaction observed by ELLA for the compounds bearing the shortest linkers, which are unable to form PNA aggregates, was further investigated by atomic force microscopy (AFM). The galactosides were grafted onto the tip of a cantilever and the PNA lectin onto a gold surface. Similar unbinding forces were registered when the valency of the ligands was increased, thus showing that the multimers cannot interact more strongly with PNA. Multiple binding events to the PNA were also never observed, thus confirming that a chelate binding mode does not operate with the multivalent galactosides, probably because the linkers are too short. Altogether, these results suggest that the cluster effect that operates in ELLA with the multimers is not related to additional PNA stabilizations and can be ascribed to local concentration effects that favor a dynamic turnover of the tethered galactosides in the PNA binding sites.
authors.affiliation: Laboratoire des Glucides FRE CNRS 3517, Institut de Chimie de Picardie, Faculté des Sciences, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex 1, France.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Almant
authors.forename: Amira
authors.initials: A
authors.lastname: Mastouri
authors.forename: Laura
authors.initials: L
authors.lastname: Gallego-Yerga
authors.forename: José Manuel
authors.initials: JM
authors.lastname: García Fernandez
authors.forename: Carmen
authors.initials: C
authors.lastname: Ortiz Mellet
authors.forename: José
authors.initials: J
authors.lastname: Kovensky
authors.forename: Sandrine
authors.initials: S
authors.lastname: Morandat
authors.forename: Karim
authors.initials: K
authors.lastname: El Kirat
authors.forename: Sébastien G
authors.initials: SG
authors.lastname: Gouin
mesh_terms: D002236:Carbohydrate Conformation; D057930:Click Chemistry; D005697:Galactosides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D019887:Peanut Agglutinin / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012995:Solubility
chemical_list: D005697:Galactosides; D019887:Peanut Agglutinin