Crystal structure of the alpha, beta, gamma-tridentate manganese complex of adenosine 5'-triphosphate cocrystallized with 2,2'-dipyridylamine.

The 1:1:1 complex of Mn2+, ATP, and 2,2'-dipyridylamine (DPA) crystallizes as Mn-(HATP)2.Mn(H2O)6.(HDPA)2.12H2O in the orthorhombic space group C222(1) with unit cell dimensions a = 10.234 (3) A, b = 22.699 (3) A, and c = 31.351 (4) A. The structure was solved by the multisolution technique and refined by the least-squares method to a final R index of 0.072 using 3516 intensities. The structure is composed of two ATP molecules sharing a common manganese atom. The metal exhibits alpha, beta, gamma coordination to the triphosphate chains of two dyad-related ATP molecules, resulting in a hexacoordinated Mn2+ ion surrounded by six phosphate groups. The metal to oxygen distances are 2.205 (6), 2.156 (4), and 2.144 (5) A for the alpha-, beta-, and gamma-phosphate groups, respectively. No metal-base interactions are observed. There is a second hexaaqua-coordinated Mn2+ ion that is also located on a dyad axis. The hydrated manganese ions sandwich the phosphate-coordinated manganese ions in the crystal with a metal-metal distance of 5.322 A. The ATP molecule is protonated on the N(1) site of the adenine base and exhibits the anti conformation (chi = 66.0 degrees). The ribofuranose ring is in the 2/3 T conformation with pseudorotation parameters P = 179 (1) degrees and tau m = 34.1 (6) degrees. The adenine bases form hydrogen-bonded self-pairs across a crystallographic dyad axis and stack with both DPA molecules to form a column along the dyad. The structure of the metal-ATP complex provides information about the possible metal coordination, conformation, and environment of the nucleoside triphosphate substrate in the enzyme.