The Influence of Lipids on the Assembly of Aquaporin Z

Abstract

The thermodynamic principles that govern the organization between lipid bilayers and membrane proteins have been studied over the past decades. Despite the many years of research on this particular topic, the forces responsible for protein folding and lateral mobility within the membrane are still poorly understood. In the following research new answers are tried to be given on this matter by studying the different oligomerization states of intrinsic membrane proteins. The Aquaporin Z (AqpZ), also called water channels, is a tetrameric intrinsic membrane protein found in Escherichia coli that will be used as a suitable model due to its well-known structure and relatively robustness. Previous studies on this subject have shown that a single amino acid (W14A) substitution in the hydrophobic interface of the AqpZ destabilizes its tetrameric form by disrupting hydrophobic interactions (V. Schmidt, ACS Omega 2017). In order to investigate the influence of lipids on the oligomerization state of the AqpZ, the protein is inserted in a large panel of liposomes differentiated by the lipid composition and ratio. The observation of the resulting AqpZ's organization in those vesicles is followed by divers biophysical methods such as fluorescence spectroscopy and electron paramagnetic resonance spectroscopy (EPR). New AqpZ cysteine mutants where designed since both techniques require highly labelled samples. The oligomerization state will be quantified by FRET signals (Fröster resonance energie transfer) and distances between monomers measured by DEER (double electron-electron resonance). Both techniques are complementary and will most certainly shed more light on how lipids influence the dynamics of membrane proteins.