Final Activity Report Summary - IMAGING SINGLE LCA S (Single-molecule interaction between calmodulin and the L-type calcium channel)
Why would one want to spy on single CaM in cells? In the past, different spying methods have been used to observe CaM in living cells: by biochemical techniques -purifying large amounts of the protein and observing its Ca2+ (by titration) and protein (by co-immunoprecipitation) binding properties and by microscopic techniques - by labelling large quantities of CaM in cells at un-natural levels and observing the cell property. We know that CaM responds to Ca2+ levels in cells, so at high calcium, CaM will fold up and bind a number of protein targets, including Calcium Channels (LCa), Calcium Pumps (PMCA), and Nitric Oxide Synthase (eNOS). However, we had previously not been good enough spies to see how fast CaM runs around in the cell, or whether CaM binds or "hides" in one place in the cell, or "sneaks" from one place to another through the cell. Such information is of importance to us because Ca2+ through CaM sends some vital messages to proteins involved in "excitation-contraction coupling" or the essence of the heart beat. Thus, CaM is involved in heart related diseases, the leading cause of death in industrialised nations in the world. From our reconnaissance, we obtain information potentially useful for drug screening and discovery.
By observing the single CaM, we unravelled some new information because the CaM was distinguishable and non-perturbing. First, the individual CaMs displayed a wide-range of motion: from extremely fast, free cytosolic motion bound to a static protein to directed motion along the cytoskeletal tracks of cells. Second, the membrane binding and motion was vastly changed upon cellular Ca2+ level changes. Third, individual CaMs were counted in co-localisation experiments to potential membrane protein binding partners and have high binding to eNOS, moderate binding to PMCA, and relatively less binding to LCa.