Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Wednesday Speaker Abstracts

Solvent Models in Protein Adsorption Simulations: Explicit, Implicit vs Experiments J. G. Vilhena 2,1 , Pamela Rubio-Pereda 1 , Ruben Perez 2 , Pedro A. Serena 1 . 1 Consejo Superior de Investigaciones Científicas - CSIC, Madrid, Spain, 2 Universidad Autonoma de Madrid, Madrid, Spain. Molecular dynamics (MD) simulations with three different solvation models, atomic force microscopy (AFM) in liquid and single-molecule force spectroscopy are combined to access the suitability of these models in describing the adsorption of ImmunoglobulinG (IgG) antibodies over a hydrophobic surface modeled with a three-layer graphene slab. The MD simulations produce two contradicting results. On one hand, two different implicit solvation models based on the generalized Born methods predict that the IgG adsorption occurs with a severe protein unfolding in less than 40ns. On the other hand, explicit solvation models predict that the IgG antibodies are strongly adsorbed, do not unfold, retain their secondary and tertiary structure upon deposition. This conundrum, widely spread on the literature, is solved here by resorting to the conclusive experimental evidence. AFM measurements of the protein height and inter-domain distances only complies with the explicit solvent simulations. In addition, single-molecule force spectroscopy demonstrate that once adsorbed the IgG is still bioactive, which is in contradiction with the severe unfolding of the IgG in the implicit solvent simulations. Therefore, these findings, clearly demonstrate the inadequacy of widely used implicit solvent in modeling the protein adsorption process. Peptides Forming Beta-Sheets on Hydrophobic Surfaces Cooperatively Promote Insulin Amyloidal Aggregation. Karim Chouchane , Myriam, Amari, Marianne Weidenhaupt, Franz Franz.Bruckert, Charlotte Vendrely. LMGP, Grenoble, France. Protein stability and aggregation is a concerning issue for pharmaceutical industry. Insulin is one of the 20 human proteins know to form amyloid fibrils. For insulin, this kind of aggregation in physiological conditions is dependent on surface adsorption. In particular hydrophobic and charged material surfaces to which insulin is exposed during its dissolution, formulation and storage can trigger amyloid fibril formation. The typical kinetic of this aggregation is divided into 3 steps: the lag phase, during which surface-adsorbed aggregation nuclei are formed, the growth phase (fast aggregation phase) and a plateau (end of aggregation phase). We study the mechanism of surface-dependent aggregation in vitro and use small adsorbed peptides as mediators (enhancers or inhibitors) of aggregation. In particular, we have shown that peptides adopting a beta-sheet structure on hydrophobic surfaces are able to accelerate insulin aggregation in a cooperative manner. The cooperativity observed is likely based on the formation of small peptide patches on the surface. These peptide patches stabilize insulin adsorption as well as their own and therefore enhance the formation of aggregation nuclei and reduce the lag time. These results may lead to a better understanding of the formation of material-surface triggered amyloid formation and can have direct applications in developing new ways of preventing therapeutic proteins from aggregation in vitro.

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