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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.