Colloquium on April 21st, 2008

Roland Netz
Physics Department, Technical University Munich

Protein adhesion, friction and unfolding: Theoretical approaches

Single-protein behavior combines the fields of non-equilibrium thermodynamics, elasticity theory and hydrodynamics. Theoretical approaches thus rely on molecular simulations, continuum modeling and scaling approaches.

This is demonstrated with a few examples:
- Spider silk consists of polypeptides with highly repetitive motives and readily adsorbs on hydrophobic and hydrophilic surfaces. Single molecule AFM studies yield adsorption energies and point to an extremely high mobility on hydrophobic surfaces. The dominant hydrophobic attraction can be quantitatively explained with classical MD simulations including explicit water. Both water structural effects and dispersion interactions contribute to this solvation attraction. [1]
- The friction coefficient of bound polymers is very low on hydrophobic substrates, which is traced back to the presence of a vacuum layer between substrate and water, which forms a lubricating cushion on which a polymer can glide. Conversely, friction forces on hydrophilic substrates are large and make determining the equilibrium binding constant in computer simulations impossible.
- Shear-flow induced unfolding of proteins plays an important role in starting the coagulation cascade in small blood vessels. In the theoretical modeling the unfolding is initiated by single-chain protrusion-like excitations and leads to a hydrodynamic unfolding transition, which is well captured by a scaling nucleation argument. [2,3]

[1] ''Peptide adsorption on a hydrophobic surface results from an interplay of solvation, surface and intrapeptide forces''
D. Horinek, A. Serr, M. Geisler, T. Pirzer, U. Slotta, S. Q. Lud, J. A. Garrido, T. Scheibel, T. Hugel, R. R. Netz
PNAS 105, 2842 (2008)

[2] ``Shear-Flow-Induced Unfolding of Polymeric Globules''
A. Alexander-Katz, M.F. Schneider, S.W. Schneider, A. Wixforth, and Roland R. Netz
Physical Review Letters, 97, 138101 (2006)

[3] ``Shear-induced unfolding triggers adhesion of von Willebrand factor fibers''
S. W. Schneider, S. Nuschele, A. Wixforth, C. Gorzelanny, A. Alexander-Katz, R. R. Netz, and M.F. Schneider
PNAS 104, 7899 (2007)