Poster Presentation The 42nd Lorne Conference on Protein Structure and Function 2017

pH- and surface pressure-depend adsorption of human apolipoprotein A1 at solid/liquid- and gas/liquid-interfaces (#137)

Susanne Dogan 1 , Michael Paulus 1 , Paul Salmen 1 , Yury Forov 1 , Christopher Weis 1 , Metin Tolan 1
  1. Technische Universität Dortmund, Fakultät Physik / DELTA , Dortmund, Germany

In natural cells, proteins face a very complex environment, in which crowding and confinement can affect the conformational stability and the adsorption behavior of proteins or even lead to aggregation. Thus, interactions of proteins with solid surfaces are major issues in a number of fields of research such as biology, medicine, or biotechnology [1, 2]. Apolipoprotein A1 (apoA1) is an important protein of high density lipoproteins (HDLs) and plays a vital role in reverse cholesterol transport. Reduced plasma levels of HDL and apoA1 are the key risk factors for atherosclerosis and cardiovascular disease [3]. Lipidfree apoA1 is the main constituent of amyloid deposits found in atherosclerotic and senile plaques, an acquired type of amyloidosis [4, 5]. We investigated the adsorption behaviour of apoA1 at hydrophilic silicon dioxide surfaces as a function of the pH-value and the surface pressure-depend adsorption behaviour at DOTMA/DOPC-monolayer by means of x-ray reflectivity (XRR). The use of the XRR method allows the analysis of buried interfaces and can be utilized to study different properties of a (multi-)layer system at interfaces, such as layer thickness, roughness and electron density. The pH-depend measurements show that apoA1 adsorbs in different conformations depending on the microenvironment. Between pH 4-pH 6, an adsorption window with different electron densities and layer thicknesses is determined. The adsorption within this window is mainly driven by electrostatic interactions. The protein is described as a molten globule with a loosely fold state [6] which is able to adsorb at the interface. With lowering the pH-value in the acidic region the protein undergoes molecular transitions in the process where α-helical segments are reduced and the protein gets into a random coil state [7]. At the cationic DOTMA/DOPC-monolayer at the gas/liquid-interface apoA1 show a reduction of the electron density without changing the layer thickness.

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