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Rabe, M. Understanding protein adsorption phenomena on solid surfaces. 2009, University of Zurich, Faculty of Science.

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Abstract

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 considerable
progress in this field there are still widely differing and even contradictive opinions on how to
explain the phenomena that are frequently observed. The present dissertation aims to advance
the understanding of 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
α-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 it is shown 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. The proposed mechanism implies increasing adsorption rates plus a
specific distribution of proteins over the surface. Both properties are experimentally
confirmed. Further, a microscopic treatment of the mechanism behind cooperativity is
realized through Monte-Carlo simulations which reproduce the experimental data accurately
and thereby confirm the suggestion that approaching proteins can be tracked to favorable
binding sites near other pre-adsorbed proteins.
In addition, phenomena related to protein adsorption include exchange mechanisms
between adsorbing and pre-adsorbed proteins, conformational and orientational
rearrangements, as well as overshooting adsorption kinetics. Another model combining these
effects is developed and tested with a strong fundament of experimental data. The primary
accomplishment related to this model is a consistent and comprehensible explanation of the
overshooting effect.
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 correlates 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 α-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.
The significance of this work results from the successful combination of substantial
experimental investigations with efficient theoretical methods giving access to a clear and
illustrative view on some exciting adsorption phenomena. Novel ideas shed light on the
diversely discussed topics of cooperative adsorption, overshooting adsorption kinetics, and
protein aggregation.

Item Type:Dissertation
Referees:Seeger S, Hamm P, Robinson J A
Communities & Collections:07 Faculty of Science > Department of Chemistry
DDC:540 Chemistry
Language:English
Date:2009
Deposited On:30 Jan 2010 18:13
Last Modified:05 Jun 2014 13:50
Number of Pages:153

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