Authors Renner, L.
Title Polymer Supported Lipid Bilayer Membranes for the Integration of Transmembrane Proteins
Date 04.05.2009
Number 3011
Abstract This work reports on the successful formation of supported multicomponent lipid bilayer membranes (sLBMs) from natural occurring lipids as well as synthetic lipids on a set of polymer cushions consisting of alternating maleic acid copolymers. Maleic acid copolymers provide a versatile platform to adjust the physico-chemical behaviour by the choice of the comonomer unit. The formation of sLBMs was triggered by a transient reduction of the electrostatic repulsion between the polymer cushions and the lipid vesicles by lowering the solutions pH to 4. Upon formation the stability of sLBMs was not affected by subsequent variations of the environmental pH to 7.2. Even drastic changes in the environmental pH (between pH 2 and pH 9) did not lead to delamination and proved the stability of the polymer sLBM. The degree of hydrophilicity and swelling of the anionic polymer cushions was found to determine both the kinetics of the membrane formation and the mobility of the lipid bilayer with lipid diffusion coefficients in the range from 0.26 to 2.6 µm2 s-1. An increase in cushion hydrophilicity correlated with a strong increase in the diffusion coefficient of the lipids. This trend was found to correlate with the kinetics of bilayer formation in the process of vesicle spreading. The observations strongly support the important role of the support’s polarity for the fluidity of the sLBM, which is probably related to the presence of a water layer between support and bilayer. The investigated polymer cushions are considered to open new options for the in situ modulation of lipid bilayer membranes characteristics to match the requirements for the successful integration of functional transmembrane proteins (TMPs). As each cushion exhibits different physico-chemical properties, the resulting behaviour of the sLBMs and TMPs could be exactly adjusted to the specific requirements of biological samples. This is exemplarily shown by the integration of the TMP beta amyloid precursor protein cleaving enzyme (BACE). Integrated BACE was observed to be mobile on all polymer cushions. On the contrary, no lateral mobility of BACE was found in solid sLBM. Furthermore, the activity of integrated BACE was analysed by the cleavage of an amyloid precursor protein analogue. Remarkably, the polymer cushions did not only enhance the mobility but were also found to increase the activity of BACE by a factor of 1.5 to 2.5 in comparison to solid sLBM. From the obtained results it is obvious that even small cytoplasmic domains of transmembrane proteins might not be preserved upon the integration in silica sLBM. The observed beneficial effects of the utilised polymer cushions on the mobility and activity of transmembrane proteins motivate further studies to clarify the general applicability of the polymer platform. Altogether, this polymer platform provides valuable options to form sLBM with varying characteristics to reconstitute transmembrane proteins for a wide range of possible future applications in biology.
Publisher Thesis
Citation Thesis (2009) 96p.
Tags polymer cushion lipid bilayer membranes qcm bace transmembrane proteins activity mobility

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