A new approach to detect membrane proteins : Loading of marker molecules into liposomes for detection of single membrane proteins

Abstract: Membrane proteins are essential to the function of biological systems. The ability to map the placement and abundance of these proteins can facilitate several improvements within both medicine and biology. This project aims to construct a new method to map specific membrane proteins in tissue by loading marker molecules into liposomes decorated with targeting molecules for detection in mass spectrometry imaging (MSI). Loaded liposomes decorated with targeting molecules would make detection of one individual membrane protein possible in the MSI. This project resulted in a loading protocol of the marker molecule n-methyl,n-ethylbenzylamine (EMBA) into liposomes. The initial loading of EMBA could be determined to be higher than the detection limit of EMBA in solution using MSI. However, due to leakage, mainly during the post insertion during decorating of the liposomes, the amount of loaded EMBA is decreased which made the detection of liposomes in the MSI more difficult. The investigation of the possibility do detect a single loaded liposome in the MSI instrument was carried out both in solution and immobilised. Preliminary results show that EMBA from the loaded liposomes can be detected in the MSI. The immobilization technique needs further refinement due to disruption of the liposome layer as a result of drying during MSI measurements. The obtained results are a great advancement towards a new technique to map membrane proteins in actual tissue using a liposome system and MSI.