The molecular basis of OH-PCB estrogen receptor activation

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.

The N-Terminus of Human Sulfotransferase 2B1b─a Sterol-Sensing Allosteric Site

“…Prior studies with human SULT1 isoforms (1A1, , 1A3, , and 1E1) reveal that these isoforms harbor an allosteric binding site through which they communicate with compounds within their metabolic domain. These sites have proven effective targets for the development of isoform-specific proto-drugs aimed at controlling isoform-related diseases.…”

“…Figure 4C presents a plot of the H6-proton line width as a function of the fraction quercetin bound ( i.e. , LW versus FB plot) for each spin label and a diamagnetic control in which the residue-247 spin-labeled PROXYL moiety is replaced by a cyclohexyl group. ,,,, LW versus FB plots for the remaining four protons can be seen in Figure S1. Each LW versus FB datapoint represents the average of three independent measurements whose errors fall within the dot diameters.…”

“…MD simulations were performed as described previously. − ,, Briefly, SWISS-MODEL was used to construct a ligand-free model of SULT2B1b from the SULT2B1b•PAP•DHEA structure (PDB 1Q22 ). GROMACS was used to protonate (pH 7.4) and energy minimize the model.…”

“…The modeling prediction that Ile 20 (seen in teal) directly contacts the hydrophobic tail of Cho is consistent with prior studies that suggested this contact 37 and demonstrated that Ile 20 is largely responsible for the high Cho selectivity of 2B1b among SULT2 isoforms. 31 Prior studies with human SULT1 isoforms (1A1, 21,22 1A3, 20,36 and 1E1 35 ) reveal that these isoforms harbor an allosteric binding site through which they communicate with compounds within their metabolic domain. These sites have proven effective targets for the development of isoform-specific proto-drugs 19 aimed at controlling isoform-related diseases.…”

“…20,22,35 The structures are highly conserved and inhibition is accomplished, as with SULT2B1b, through stabilization of the closed form of the active-site cap. 19,20,35,61 The high degree of sequence and structural conservation in the SULT1 family suggests other family members harbor a similar allosteric pocket. In contrast, among the SULT2 isoforms (2A1, 2B1a, and 2B1b) only 2B1b has evolved the capacity for catechin regulation, which, as described above, is conferred by its lengthened N-terminus.…”