Single-molecule analysis of synaptotagmin 7 lateral diffusion across a supported lipid bilayer

Synaptotagmin 7 is an important protein involved with insulin secretion in pancreatic beta-cells. It acts as a Ca2+ sensor for the SNAREs protein that facilitates the fusion between the secretory vesicle and the plasma membrane. Synaptotagmin 7 binds to the calcium using its two C2 domains, the C2A and the C2B. TIRFM was used to test the diffusion coefficient of Syt 7 C2 domains across a supported lipid bilayer in order to further understand how they bind to membranes. Should both the C2 domains bind with the same orientation as each other, then the frictional coefficient should become additive as the linker length between them lengthens and approach the free draining limit. Results show that the diffusion coefficient is not additive despite the elongated linker length. This leads to the plausible explanation that the C2 domains interact with each other when bound to a lipid bilayer. Further research would delve into this interaction between the two C2 domains.