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 3 alpha-phenol group of estrogenic steroids such as estradiol (E-2), The recent crystal structure of EST adenosine 3',5'-diphosphate (PAP)- E-2 complex has revealed that residues Lys(48), Thr(45) Thr(51), Thr(52), Lys(106), His(108), and Try(240) 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 Lys(48), Lys(106), or His(108) nearly abolishes EST activity, indicating that they play a critical role in catalysis, A present 2.2-A 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 ) and a possible water molecule (2.3 Angstrom), This water molecule superimposes well to the 3 alpha-phenol group of E-2 in the crystal structure of the EST . PAP . E-2 complex. These structures are characteristic of the transition state for an in-line sulfuryl transfer reaction from PAPS to E-2. Moreover, residues Lys(48), Lys(106), His(108) are found to be coordinated with the vanadate molecule at the transition state of EST.