  4.2.3.61 | to 2.2-2.8 A resolution, of TEAS alone and in complexes with two different substrate analogs. TEAS consists entirely of alpha-helices and short connecting loops and turns, and is organized into two structural domains. Two Mg2+ ions are coordinated on opposite sides of the entrance to the active site pocket, and constitute a diphosphate binding site. Asp301 coordinates a Mg2+ in the native TEAS structure, and the side chain carboxyl of Glu379 provides a longer range interaction. Asp305 provides an additional coordination bond in the enzyme with substrate analogs bound. Asp301 and Asp305 are part of a -DDXXD- sequence. Asp301 directly contacts Mg2+, whereas Asp302 demonstrates no direct metal coordination. The side chains of Asp444, Thr448, Glu452, and one water molecule the second coordinate Mg2+. In the native TEAS structure, the A-C and J-K loops and the residues NH2-terminal of residue 36 are disordered |
