title: Stabilization of Insulin by Adsorption on a Hydrophobic Silane Self-Assembled Monolayer.
abstract: The interaction between many proteins and hydrophobic functionalized surfaces is known to induce β-sheet and amyloid fibril formation. In particular, insulin has served as a model peptide to understand such fibrillation, but the early stages of insulin misfolding and the influence of the surface have not been followed in detail under the acidic conditions relevant to the synthesis and purification of insulin. Here we compare the adsorption of human insulin on a hydrophobic (-CH3-terminated) silane self-assembled monolayer to a hydrophilic (-NH3(+)-terminated) layer. We monitor the secondary structure of insulin with Fourier transform infrared attenuated total reflection and side-chain orientation with sum frequency spectroscopy. Adsorbed insulin retains a close-to-native secondary structure on both hydrophobic and hydrophilic surfaces for extended periods at room temperature and converts to a β-sheet-rich structure only at elevated temperature. We propose that the known acid stabilization of human insulin and the protection of the aggregation-prone hydrophobic domains on the insulin monomer by adsorption on the hydrophobic surface work together to inhibit fibril formation at room temperature.
authors.affiliation: †Department of Chemistry, Surface Science Research Centre, University of Liverpool, Oxford Road, Liverpool L69 3BZ, U.K.|‡Molecular Spectroscopy Group, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Sergio
authors.initials: S
authors.lastname: Mauri
authors.affiliation: †Department of Chemistry, Surface Science Research Centre, University of Liverpool, Oxford Road, Liverpool L69 3BZ, U.K.
authors.forename: Martin
authors.initials: M
authors.lastname: Volk
authors.affiliation: §Covance Inc., Willowburn Avenue, Alnwick NE66 2JH, U.K.
authors.forename: Stephen
authors.initials: S
authors.lastname: Byard
authors.forename: Harald
authors.initials: H
authors.lastname: Berchtold
authors.affiliation: †Department of Chemistry, Surface Science Research Centre, University of Liverpool, Oxford Road, Liverpool L69 3BZ, U.K.
authors.forename: Heike
authors.initials: H
authors.lastname: Arnolds
mesh_terms: D000327:Adsorption; D057927:Hydrophobic and Hydrophilic Interactions; D007328:Insulin / Q000737:chemistry*; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry; D012821:Silanes / Q000138:chemical synthesis* / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature
chemical_list: D007328:Insulin; D011506:Proteins; D012821:Silanes