Dimerization Is Responsible for the Structural Stability of Human Sulfotransferase 1A1

Abstract

ABSTRACT:Cytosolic sulfotransferases (SULTs) are responsible for the metabolism of a variety of drugs, xenobiotics, and endogenous compounds. Most cytosolic SULTs are found to be homodimers. However, transformation between monomeric and dimeric SULTs can be achieved by a single amino acid mutation. The importance of quaternary structure for cytosolic sulfotransferase was investigated using recombinant human SULT1A1, a homodimer, and its monomeric mutant (V270E). The differences between dimeric and monomeric SULT1A1 were examined by size-exclusion liquid chromatography, enzyme kinetics, substrate binding affinity, thermal inactivation, conformational stability, and circular dichroism. Variations, especially on their secondary structures and stability, between homodimer and monomer of human SULT1A1 were observed. It was found that the active site of SULT1A1 was not significantly perturbed after the change of its quaternary structure according to SULT1A1 kinetics and substrate binding affinity. However, the stability of monomeric SULT1A1 is significantly decreased. We proposed that the importance of human SULT1A1 as a homodimer was to maintain its structural stability, and the change of secondary structure was responsible for alternating its quaternary structure.

Structural plasticity in the human cytosolic sulfotransferase dimer and its role in substrate selectivity and catalysis

“…This allosteric site was identified by the ability of two substrate molecules to dock into the active site of the open hSULT2A1 enzyme [48,138]. Another report describes the loss of integrity of hSULT1A1 due to monomerization [137]. Our own observations regarding the integrity of a hSULT1B1 monomeric isoform support these results.…”

“…Despite this promising hypothesis, unpublished data now indicate that various combinations of PAPS and substrate do not affect the dimer status of hSULT2A1, implying the interface is maintained through the entire catalytic cycle of the SULTs unlike EGFR [96]. Multiple studies, including our own unpublished work involving hSULT1B1, have shown that monomeric SULT isoforms retain a high level of activity [137,138]. Aside from changes in activity levels, minimal differences between monomeric and dimeric SULT isoforms have been described.…”

Comparison of murine and human estrogen sulfotransferase inhibition in vitro and in silico—Implications for differences in activity, subunit dimerization and substrate inhibition

“…The same has also been observed for substrate affinity Pedersen 2002;Lu 2008;Lu 2009). Lu et al suggest that the main role for dimerization of sulfotransferases could be to maintain structural stability (Lu 2009). …”

“…Zhang et al (Zhang 1998) proposed that one of the binding sites in the hSULT1E1 dimer is catalytic and the other site is allosteric and regulates turnover. However, it has also been shown that activity, affinity and substrate inhibition are independent of subunit dimerization Pedersen 2002;Lu 2008;Lu 2009). It has been suggested that the role of dimerization is to maintain structural stability (Lu 2009).…”

“…However, it has also been shown that activity, affinity and substrate inhibition are independent of subunit dimerization Pedersen 2002;Lu 2008;Lu 2009). It has been suggested that the role of dimerization is to maintain structural stability (Lu 2009). The simulations performed in this study show no differences in ligand (E2) movement or interactions in the hSULT1E1 monomer and dimer.…”