Structure of 5-formyltetrahydrofolate cyclo-ligase from Bacillus anthracis (BA4489)

Meier, C.; Carter, L.G.; Winter, G.; Owens, R.J.; Stuart, D.I.; Esnouf, R.M.

doi:10.1107/S1744309107007221

Figure 3
The mechanism of catalysis by B. anthracis 5-formyl-THF cyclo-ligase. (a) A cut-through of the 5-formyl-THF cyclo-ligase structure showing the cofactor/substrate-binding pocket with bound ADP and phosphate. The enlarged view shows 2F_o - F_c electron density contoured at 1.5 [sigma]

(green) for these moieties. Weak electron density (not shown) suggests that the substrate/product binds in the right-hand side of this pocket. (b) A ball-and-stick diagram showing the octahedral coordination of the Mg²⁺ ion by the [alpha]

- and

-phosphates of ADP, residues Asp144 and Asp173 and two tightly bound water molecules. Interaction distances are shown in Å. This coordination helps orient the [gamma]

-phosphate of ATP correctly for attack on the 5-formyl-THF. The green lines show 2F_o - F_c electron density contoured at 2.2 [sigma]

. (c) The proposed catalytic mechanism of B. anthracis 5-formyl-THF cyclo-ligase via a phospho-enol intermediate. Our structure represents the final stage of the process, after the product has dissociated from the binding pocket.