The Transition of Human Estrogen Sulfotransferase from Generalist to Specialist Using Directed Enzyme Evolution

Broad specificity is believed to be a property of primordial enzymes that diverged during natural protein evolution to produce highly specific and efficient enzymes. Human estrogen sulfotransferase (SULT1E1) is a broad-specificity enzyme that detoxifies a variety of chemicals, including estrogens, by the transfer of sulfate. To study the molecular basis for the broad specificity of this enzyme and to investigate the process of SULT1E1 specialization, we have adopted a directed enzyme evolution approach. Using two iterative rounds of evolution, we generated SULT1E1 mutants with increased thermostability and narrower specificity from the broadly specific wild-type enzyme. To identify mutants with enhanced specificity, we developed an unbiased screening assay to assess sulfate transfer to three different acceptors in parallel. Such an assay enabled the isolation of SULT1E1 mutants with enhanced or wild-type activity toward an estrogen acceptor and significantly reduced activity for phenol or coumarin type of acceptors, leading to up to 3 orders of magnitude increase in specificity. We found that mutations conferring novel specificity are located in the vicinity of the active site and thus may play a direct role in reshaping the acceptor-binding site. Finally, such mutations resulted in reduced SULT1E1 thermostability, revealing a trade-off between SULT1E1 thermostability and acquisition of novel function. [Display omitted] ► Cytosolic sulfotransferases (SULTs) play a central role in the detoxification of exogenous and endogenous compounds including essential hormones. ► To study the molecular basis for SULT1E1 broad specificity, we used directed evolution approaches. ► We generated SULT1E1 mutants with increased specificity, exhibiting decreased activity for promiscuous acceptors and increased activity for 17β estradiol. ► The directed evolution process revealed a trade-off in SULT1E1 between obtaining new specificity and thermostability. ► Our work sheds new light on the SULT1E1 mechanism of substrate discrimination and evolution.