Investigating the effect of salt concentrations on the immune cell membrane protein CD45 D1-D4 in a supported lipid bilayer using hydrodynamic trapping
Abstract: The immune system is a very complex system, aimed to protect the body from the many dangers that loom around us. A well-functioning immune system can fight of most invaders, remove foreign particles that entered our bodies, and take care of dead cells. The aim in this work is seeing how the protein CD45 (also known as PTPRC, protein tyrosine phosphatase, receptor type, C) is affected by salt concentration, more exactly how it is oriented on a lipid bilayer. CD45 have been observed to be essential for proper activation of T cells, but exactly how this is achieved on a molecular level is not known. Since the protein interact with its environment, its orientation may play an important role for the sensitivity and function of CD45. In order to investigate this, a combination of total internal reflection fluorescence microscopy, FRAP (fluorescence recovery after photobleaching) and hydrodynamic trapping have been used. The protein was attached to a supported lipid bilayer (SLB), which is a common cell membrane mimic. The orientation of the protein, i.e. its effective height, on the bilayer was measured using hydrodynamic trapping at different concentrations of sodium chloride at a physiological pH of 7.4. The diffusion of the protein across the SLB was also studied at different salt concentrations. The investigation implied a difference in the height of the proteins with it standing higher above the bilayer with increased salt concentration. This finding is important since it has consequences for how CD45 should be modelled on cell membrane mimics such as SLBs as well as on live cells.
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