Factors influencing the thermal stability of the bacterial water channel AqpZ and their functional consequences

Description

Lipid-protein interactions are crucial in determining the stability and function of transmembrane proteins. The interactions that occur at the lipid-protein interface or bilayer properties can affect protein conformation. Protein oligomerization can lead to structural and proteolytic stability, functional diversity, regulatory mechanisms, and the formation of binding cavities. However, the contributions of lipidprotein
interactions and oligomerization to membrane protein stability remain unclear. We aimed to examine the contributions of the oligomeric assembly and specific lipid interactions on the thermal stability of AqpZ, a tetrameric bacterial water channel. To investigate this, we compared the wild-type protein to a de novo-designed protein variant with decreased oligomeric stability and increased monomeric stability, both reconstituted into three different lipid compositions. To examine the interplay between protein stability and function we also utilized purified and reconstituted AQPZ to estimate quantitative water permeability values via a combination of stopped-flow assays, fluorescence correlation spectroscopy and dynamic light scattering. Our results show that the tetrameric assembly is the primary determinant of thermal stability. Furthermore, both variants were more stable in the nature-like lipid environment (PLE) than simplified lipid mixtures, indicating the importance of lipid tail complexity in protein stability. The effect of cardiolipin on protein stability was more pronounced in the destabilized AqpZ variant. Interestingly, in contrast to the importance of lipid chain complexity for protein stability, cardiolipin seems essential for protein function, as indicated by an increased single-channel water permeability similar to PLE. These findings improve our understanding of the structurefunction relationship of oligomeric transmembrane channels and aid the development of optimized AqpZ variants for use in synthetic biology.

Period	09 Jul 2024
Event title	Biophysics Austria Conference 2024, Salzburg 8-10 July 2024
Event type	Conference
Location	AustriaShow on map