The goal of the project was to obtain experimental evidence for the hypothesis that chemiosmotic coupling with sodium (or other larger molecules) rather than proton gradients would be advantageous for LUCA, the Last Common Universial Ancestor. LUCA did not have phospholipids typical of biological membranes but its membrane was most likely composed of simple amphiphiles such as fatty acids. Furthermore, could hydrophobic proteins and peptides function in such membranes.
The permeability of membranes for ions and solutes was determined using a previously developed method [1]. Fatty acid membranes and hybrid membranes composed of lipids and varying amounts of fatty acids were prepared and tested. In all cases, fatty acids increased the permeability and instability of the membranes but solute gradients could be maintained for relevant time periods in hybrid membranes with up to 50% fatty acids. Remarkably, membrane proteins such as the mitochondrial ATP/ADP carrier and the Na+/H+ antiporter MjNhaA1 could be functionally reconstituted in hybrid membranes, using Perceval HR as fluorescent reporter of the ATP/ADP ratio and pyranine as probe for pH inside the vesicles. Gradients could be generated in hybrid membranes but not in vesicles solely composed of fatty acids, and, as anticipated, the membrane proteins were not functional in fatty acid membranes.
Due to health problems, the project could not be completed and was terminated on 30 April 2024. Sadly, Sagar Raturi had to stop his scientific career.
1. Frallicciardi J, Gabba M & Poolman B (2021) Measuring small molecule permeation through biological membranes. Nat Protoc 17: 2620-2646. doi: 10.1038/s41596-022-00734-2
