Structural rearrangement of SULT2A1: effects on dehydroepiandrosterone and raloxifene sulfation

Abstract

BACKGROUND: Human cytosoloic sulfotransferase (SULT) 2A1 is a major hepatic isoform and sulfates hydroxyl groups in structurally diverse sterols and xenobiotics. SULT2A1 crystal structures resolved in the presence and absence of 3',5'-diphosphoadenosine (PAP) or dehydropeiandrosterone (DHEA) suggest a significant rearrangement of the peptide that forms the surface of the active site in the presence of PAP. MATERIALS AND METHODS: Molecular modeling was used to examine the effects of the rearrangement in SULT2A1 associated with 3'-phosphoadenosine 5'-phosphosulfate (PAPS) binding on the binding of DHEA and raloxifene. The kinetics of DHEA and raloxifene sulfation was analyzed to investigate the effects of the rearrangement on SULT2A1 activity. RESULTS: Molecular models indicate that DHEA is able to bind to SULT2A1 in both conformations (open, without PAP; closed, with PAP) in a catalytic configuration, whereas raloxifene bound in a catalytic conformation only in the open structure. Raloxifene did not bind in the smaller, closed substrate binding pocket. Kinetic analysis of DHEA sulfation was consistent with a random Bi-Bi reaction mechanism, whereas raloxifene sulfation was more indicative of an ordered reaction mechanism with raloxifene binding first. Initial burst kinetics with DHEA yielded similar results after preincubation of SULT2A1 with DHEA or PAPS. Preincubation of SULT2A1 with raloxifene showed a burst of raloxifene sulfate formation with the addition of PAPS. In contrast, little raloxifene sulfate was formed if SULT2A1 was preincubated with PAPS and the reaction initiated with raloxifene. CONCLUSIONS: The structural rearrangements in SULT2A1 caused by PAPS binding can alter the sulfation mechanism and kinetics of different substrates.