The dynamic behavior of annexin V as a function of calcium ion binding: a circular dichroism, UV absorption, and steady-state and time-resolved fluorescence study

Steady-state and time-resolved fluorescence, circular dichroism and ultraviolet (UV)-difference spectroscopy studies indicate the tryptophan 187 in the domain III of annexin V is required for calcium ion binding. Trp 187 exhibits an excited-state reaction that causes hydrogen bond formation in the alpha-carbonyl groups of Thr224. Trp 187 is not seen in crystal structures with high level of calcium ions indicating structural changes that enable the incorporation of the protein on phospholipid membranes.