The molecular basis of OH-PCB estrogen receptor activation

Ting Wang,Ian Cook,Thomas S Leyh

doi:10.1016/j.jbc.2021.100353

Ting Wang, Ian Cook + Show 1 more

Open Access

https://doi.org/10.1016/j.jbc.2021.100353

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Abstract

Polychlorinated bisphenols (PCBs) continue to contaminate food chains globally where they concentrate in tissues and disrupt the endocrine systems of species throughout the ecosphere. Hydroxylated PCBs (OH-PCBs) are major PCB metabolites and high-affinity inhibitors of human estrogen sulfotransferase (SULT1E1), which sulfonates estrogens and thus prevents them from binding to and activating their receptors. OH-PCB inhibition of SULT1E1 is believed to contribute significantly to PCB-based endocrine disruption. Here, for the first time, the molecular basis of OH-PCB inhibition of SULT1E1 is revealed in a structure of SULT1E1 in complex with OH-PCB1 (4ʹ-OH-2,6-dichlorobiphenol) and its substrates, estradiol (E2), and PAP (3’-phosphoadenosine-5-phosphosulfate). OH-PCB1 prevents catalysis by intercalating between E2 and catalytic residues and establishes a new E2-binding site whose E2 affinity and positioning are greater than and competitive with those of the reactive-binding pocket. Such complexes have not been observed previously and offer a novel template for the design of high-affinity inhibitors. Mutating residues in direct contact with OH-PCB weaken its affinity without compromising the enzyme’s catalytic parameters. These OH-PCB resistant mutants were used in stable transfectant studies to demonstrate that OH-PCBs regulate estrogen receptors in cultured human cell lines by binding the OH-PCB binding pocket of SULT1E1.

Highlights

The SULT1E1 isoform plays a pivotal role in regulating the cellular activities of estrogens
To better understand the molecular basis of OH-polychlorinated biphenyls (PCB) action, and with the intent to use the findings as a template for the design and synthesis of potent SULT1E1-specfic inhibitors, we determined the solution structure of SULT1E1 bound to 30- phosphoadenosine 50-phosphate (PAP), estradiol (E2), and OH-PCB1 (Fig. 1)
OH-PCB1 was selected because its exchange rate is well suited to the NMR line-broadening methods used in the structural studies described below

Summary

Introduction

The SULT1E1 isoform plays a pivotal role in regulating the cellular activities of estrogens. To assess whether mutagenizing OH-PCB1 binding-site residues influences the catalytic functions of SULT1E1, the effects of such mutations on the initial-rate parameters (Km and kcat) of 1-hydroxypyrene (1-HP, a fluorescent E2-like substrate [51, 52]) were determined (see, Experimental procedures). Conditions: SULT1E1 (15 nM, active sites), OH-PCB1 (12.5–1000 nM), E2 (4.0 μM), PAP (0, black dots, or 300 μM (100 × Kd) red dots), KPO4 (50 mM), pH 7.4, 25 C ± 2 deg.

Results

Conclusion