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29

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.