title: Human insulin adsorption kinetics, conformational changes and amyloidal aggregate formation on hydrophobic surfaces.
abstract: The formation of insulin amyloidal aggregates on material surfaces is a well-known phenomenon with important pharmaceutical and medical implications. Using surface plasmon resonance imaging, we monitor insulin adsorption on model hydrophobic surfaces in real time. Insulin adsorbs in two phases: first, a very fast phase (less than 1 min), where a protein monolayer forms, followed by a slower one that can last for at least 1h, where multilayered protein aggregates are present. The dissociation kinetics reveals the presence of two insulin populations that slowly interconvert: a rapidly dissociating pool and a pool of strongly bound insulin aggregates. After 1h of contact between the protein solution and the surface, the adsorbed insulin has practically stopped dissociating from the surface. The conformation of adsorbed insulin is probed by attenuated total reflection-Fourier transform infrared spectroscopy. Characteristic shifts in the amide A and amide II' bands are associated with insulin adsorption. The amide I band is also distinct from that of soluble or aggregated insulin, and it slowly evolves in time. A 1708 cm⁻¹ peak is observed, which characterizes insulin adsorbed for times longer than 30 min. Finally, Thioflavin T, a marker of extended β-sheet structures present in amyloid fibers, binds to adsorbed insulin after 30-40 min. Altogether, these results reveal that the conformational change induced in insulin upon binding to hydrophobic surfaces allows further insulin binding from the solution. Adsorbed insulin is thus an intermediate along the α-to-β structural transition that results in the formation of amyloidal fibers on these material surfaces.
authors.affiliation: Laboratoire des Matériaux et du Génie Physique, Phelma-Minatec, 3 Parvis Louis Néel, BP257, F-38016 Grenoble Cedex, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Nault
authors.forename: Perry
authors.initials: P
authors.lastname: Guo
authors.forename: Bhagyashree
authors.initials: B
authors.lastname: Jain
authors.forename: Yves
authors.initials: Y
authors.lastname: Bréchet
authors.forename: Franz
authors.initials: F
authors.lastname: Bruckert
authors.forename: Marianne
authors.initials: M
authors.lastname: Weidenhaupt
mesh_terms: D000327:Adsorption; D000682:Amyloid / Q000737:chemistry*; D002138:Calibration; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007328:Insulin / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D020836:Protein Structure, Quaternary; D017550:Spectroscopy, Fourier Transform Infrared; D020349:Surface Plasmon Resonance; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000682:Amyloid; D007328:Insulin