Abstract: The activation of T cells of the immune system requires intact plasma membrane. We aim to study the effect of transmembrane domains of four selected proteins involved in the activation of T cells, CD3e, CD3z, LAT and PAG-85, on the dynamic membrane organisation. The influence of transmembrane domain-derived peptides on physical properties of the membrane lipids, such as acyl chain ordering, will be analysed in model systems. Diffusion of these peptides in membranes with different lipid composition will be tested. Finally, the diffusion and clustering of the fluorescent fusion proteins containing the transmembrane domains of the proteins expressed in T cells will be compared to their full-length counterparts. This will allow us to distinguish the effects caused by the transmembrane domains from that of the other parts of the proteins. Altogether, the proposed project should add to the discussion on the forces involved in the dynamic compartmentalisation of cellular membranes, the phenomenon essential for the proper signalling in cells.