NMR analyses of the interactions of human annexin I with ATP, Ca2+, and Mg2+.

Human annexin I is a member of the annexin family of calcium-dependent phospholipid binding proteins. The structure of an N-terminally truncated human annexin I (delta-annexin I) and its interactions with Ca2+, Mg2+, and ATP were studied at the atomic level using nuclear magnetic resonance (NMR) spectroscopy. Since delta-annexin I is a large protein, with a molecular weight of 35 kDa, a site-specific (carbonyl-13C, amide-15N) labeling technique was used to determine the interaction sites of delta-annexin I with Ca2+, Mg2+, and ATP. The 13C NMR study focused on the carbonyl carbon resonances of the histidine residues of delta-annexin I. We found that ATP binds to delta-annexin I, and that the ATP binding site is located in the 1-domain of annexin I. We also found that histidine-52 is involved in that site, and that the binding ratio of ATP to delta-annexin I is 1:1.