The sulfuryl transfer mechanism. Crystal structure of a vanadate complex of estrogen sulfotransferase and mutational analysis

Estrogen sulfotransferase (EST) catalyzes transfer of the 5'-sulfuryl group of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) to the 3α-phenol group of estrogenic steroids such as estradiol (E₂). The recent crystal structure of EST-adenosine 3',5'-diphosphate (PAP)- E₂ complex has revealed that residues Lys⁴⁸, Thr⁴⁵, Thr⁵¹, Thr⁵², Lys¹⁰⁶, His¹⁰⁸, and Try²⁴⁰ are in position to play a catalytic role in the sulfuryl transfer reaction of EST (Kakuta Y., Pedersen, L. G., Carter, C. W., Negishi, M., and Pedersen, L. C. (1997) Nat. Struct. Biol. 4, 904-908). Mutation of Lys⁴⁸, Lys¹⁰⁶, or His¹⁰⁸ nearly abolishes EST activity, indicating that they play a critical role in catalysis. A present 2.2-Å resolution structure of EST-PAP-vanadate complex indicates that the vanadate molecule adopts a trigonal bipyramidal geometry with its equatorial oxygens coordinated to these three residues. The apical positions of the vanadate molecule are occupied by a terminal oxygen of the 5'-phosphate of PAP (2.1 Å) and a possible water molecule (2.3 Å). This water molecule superimposes well to the 3α-phenol group of E₂ in the crystal structure of the EST·PAP·E₂ complex. These structures are characteristic of the transition state for an in-line sulfuryl transfer reaction from PAPS to E₂. Moreover, residues Lys⁴⁸, Lys¹⁰⁶, and His¹⁰⁸ are found to be coordinated with the vanadate molecule at the transition state of EST.