Proteins & Surfaces

Unravel Protein Adsorption at Solid Surfaces

Protein adsorption at solid surfaces plays a key role in many natural processes and has therefore promoted a widespread interest in many research areas. Despite consid

erable progress in this field there are still widely differing and even contradictive opinions on how to explain the phenomena that are frequently observed. The goal of the project is to understand protein adsorption and to systematically unravel the underlying molecular mechanism. This is achieved by acquiring and evaluating comprehensive experimental data sets using fluorescence sensing and imaging methods. Experiments are conducted on model systems comprising the proteins BSA, Fibrinogen, β-Lactoglobulin, and a-Synuclein, hydrophilic and hydrophobic surfaces and varying pH and ionic strength conditions.

One of the comprehensively studied adsorption phenomena is cooperativity which refers to the effect that the adsorption of proteins is enhanced by the presence of pre-adsorbed proteins. Contradicting a widespread opinion we could show for the first time that cooperativity is not necessarily associated with the growth of tight surface aggregates. Instead, a macroscopic model description is suggested that simply assumes the overlap of two parallel adsorption pathways, one for the adsorption at isolated surface positions and one for the adsorption near other surface-bound proteins.

Finally, the behavior of protein aggregates or clusters on surfaces is explored. Protein clusters can form spontaneously in the solution and subsequently deposit onto the surface. For the first time it was shown that induced by protein-surface interactions freshly deposited protein clusters start to spread in order to maximize the contact area between proteins and surface. The spreading rate is considerably faster on hydrophobic surfaces as compared to hydrophilic surfaces which correlate with the lateral mobility of the protein monomers on theses surfaces. Interestingly, on a hydrophobic surface a spreading protein cluster can even rupture a pre-adsorbed protein monolayer by displacing the monomers from the area that it is about to occupy. Inversely to protein aggregation in solution, the direct growth of aggregates on the surface can also be observed using the protein a-Synuclein which is the pathological component of Parkinson’s disease. Whereas the on-surface growth mechanism is the typically proposed one when protein aggregates are detected on a surface, the discovery that protein aggregates can also come from the solution and spread on the surface opens a completely new perspective on this topic. Experimental strategies to distinguish between these two different mechanisms are comprehensively discussed.