Immobilizing single lipid and channel molecules in artificial lipid bilayers with annexin A5

The effects of annexin A5 on the lateral diffusion of single-molecule lipids and single-molecule proteins were studied in an artificial lipid bilayer membrane. Annexin A5 is a member of the annexin superfamily, which binds preferentially to anionic phospholipids in a Ca²⁺-dependent manner. In this report, we were able to directly monitor single BODIPY 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and ryanodine receptor type 2 (RyR2) labeled with Cy5 molecules in lipid bilayers containing phosphatidylserine (PS) by using fluorescence microscopy. The diffusion coefficients were calculated at various annexin A5 concentrations. The diffusion coefficients of BODIPYDHPE and Cy5-RyR2 in the absence of annexin A5 were 4.81 × 10^-8 cm²/s and 2.13 × 10^-8 cm²/s, respectively. In the presence of 1 μM annexin A5, the diffusion coefficients of BODIPY-DHPE and Cy5-RyR2 were 2.2 ×10 ^-10 Cm²/s and 9.5 × 10^-11 cm ²/s and 9.5 × 10^-11 cm²/s, respectively. Overall, 1 μM of annexin A5 was sufficient to induce a 200-fold decrease in the lateral diffusion coefficient. Additionally, we performed electrophysiological examinations and determined that annexin A5 has little effect on the function of RyR2. This means that annexin A5 can be used to immobilize RyR2 in a lipid bilayer when imaging and analyzing RyR2.