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Dimeric human sulfotransferase 1B1 displays cofactor-dependent subunit communication.

Tibbs ZE, Falany CN - Pharmacol Res Perspect (2015)

Bottom Line: While SULT dimerization is highly conserved, the necessity for the interaction has not been established.The results suggest the dimer subunits may possess the capability of communicating with one another in a manner dependent on the presence of the cofactor.These results suggest SULT dimerization may be important in maintaining cofactor binding/release properties of SULTs and provide hypothetical explanations for SULT half-site reactivity and substrate inhibition, which can be analyzed in vitro.

View Article: PubMed Central - PubMed

Affiliation: The Department of Pharmacology and Toxicology, The University of Alabama at Birmingham Birmingham, Alabama, 35294-0019.

ABSTRACT
The cytosolic sulfotransferases (SULTs) are dimeric enzymes that catalyze the transformation of hydrophobic drugs and hormones into hydrophilic sulfate esters thereby providing the body with an important pathway for regulating small molecule activity and excretion. While SULT dimerization is highly conserved, the necessity for the interaction has not been established. To perform its function, a SULT must efficiently bind the universal sulfate donor, 3'-phosphoadenosine-5'-phosphosulfate (PAPS), and release the byproduct, 3', 5'-diphosphoadenosine (PAP), following catalysis. We hypothesize this efficient binding and release of PAPS/PAP may be connected to SULT dimerization. To allow for the visualization of dynamic protein interactions critical for addressing this hypothesis and to generate kinetically testable hypotheses, molecular dynamic simulations (MDS) of hSULT1B1 were performed with PAPS and PAP bound to each dimer subunit in various combinations. The results suggest the dimer subunits may possess the capability of communicating with one another in a manner dependent on the presence of the cofactor. PAP or PAPS binding to a single side of the dimer results in decreased backbone flexibility of both the bound and unbound subunits, implying the dimer subunits may not act independently. Further, binding of PAP to one subunit of the dimer and PAPS to the other caused increased flexibility in the subunit bound to the inactive cofactor (PAP). These results suggest SULT dimerization may be important in maintaining cofactor binding/release properties of SULTs and provide hypothetical explanations for SULT half-site reactivity and substrate inhibition, which can be analyzed in vitro.

No MeSH data available.


Related in: MedlinePlus

Transition of the dimeric SULT between cofactor binding-states. Yellow triangle = PAPS, red triangle = PAP, yellow arrow = PAPS binding/release, orange arrow = catalysis, red arrow = PAP binding/release.
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fig11: Transition of the dimeric SULT between cofactor binding-states. Yellow triangle = PAPS, red triangle = PAP, yellow arrow = PAPS binding/release, orange arrow = catalysis, red arrow = PAP binding/release.

Mentions: To result in half-site reactivity, PAPS-induced cross talk must alter the PAPS-binding affinity or diminish the catalytic competency of the neighboring subunit. At least one report exists in which two distinct PAPS-binding affinities were observed for a dimeric rat sulfotransferase isoform, aryl sulfotransferase IV, suggesting PAPS binding to a single subunit induces structural changes in the dimeric subunit that alter the second site’s affinity for PAPS (Marshall et al. 1997). If only a single subunit is bound to PAPS, catalysis would be immediately followed by a state in which one dimer subunit is bound to PAP and the sulfated product. To the best of our knowledge, the effect of PAP’s presence in a single side of the dimer on the binding of PAPS to the second subunit has not been reported. After catalysis at the first site, the substrate and PAPS may bind with high affinity at the second site. After binding occurs at the second site, the first subunit may have to release PAP or “wait” for PAP to shift its orientation before the neighboring subunit is rendered catalytic. The shift in orientation of PAP in simulation [6] and unhinging of Loop 3 could be an integral part of this mechanism allowing the PAPS bound subunit to favor catalysis, while PAP release is favored in the dimer subunit. The favorable release of PAP, stimulated by PAPS’ presence in the neighboring subunit, could arm the SULT dimer with an oscillating mechanism as depicted in Figure11. When considering an in vitro environment where SULT and PAPS are incubated together prior to the addition of substrate, the dimer is free to bind either one or two molecules of PAPS depending on the concentration (Panel B or D). In either case, upon addition of substrate, a single subunit of the half-site reactive enzyme catalyzes sulfuryl transfer, forming PAP (Panel C or E). The enzyme is now free for PAPS to bind the neighboring subunit (Panel E). As illustrated in simulation [6], bound PAPS may stimulate an increase in Loop 3 flexibility in the PAP bound chain, favoring release of PAP, reestablishing a dimer complex with only one subunit bound to PAPS (panel B). This binding and release pattern can progress, oscillating between three distinct states, panels B, C, and E (Fig.11).


Dimeric human sulfotransferase 1B1 displays cofactor-dependent subunit communication.

Tibbs ZE, Falany CN - Pharmacol Res Perspect (2015)

Transition of the dimeric SULT between cofactor binding-states. Yellow triangle = PAPS, red triangle = PAP, yellow arrow = PAPS binding/release, orange arrow = catalysis, red arrow = PAP binding/release.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492763&req=5

fig11: Transition of the dimeric SULT between cofactor binding-states. Yellow triangle = PAPS, red triangle = PAP, yellow arrow = PAPS binding/release, orange arrow = catalysis, red arrow = PAP binding/release.
Mentions: To result in half-site reactivity, PAPS-induced cross talk must alter the PAPS-binding affinity or diminish the catalytic competency of the neighboring subunit. At least one report exists in which two distinct PAPS-binding affinities were observed for a dimeric rat sulfotransferase isoform, aryl sulfotransferase IV, suggesting PAPS binding to a single subunit induces structural changes in the dimeric subunit that alter the second site’s affinity for PAPS (Marshall et al. 1997). If only a single subunit is bound to PAPS, catalysis would be immediately followed by a state in which one dimer subunit is bound to PAP and the sulfated product. To the best of our knowledge, the effect of PAP’s presence in a single side of the dimer on the binding of PAPS to the second subunit has not been reported. After catalysis at the first site, the substrate and PAPS may bind with high affinity at the second site. After binding occurs at the second site, the first subunit may have to release PAP or “wait” for PAP to shift its orientation before the neighboring subunit is rendered catalytic. The shift in orientation of PAP in simulation [6] and unhinging of Loop 3 could be an integral part of this mechanism allowing the PAPS bound subunit to favor catalysis, while PAP release is favored in the dimer subunit. The favorable release of PAP, stimulated by PAPS’ presence in the neighboring subunit, could arm the SULT dimer with an oscillating mechanism as depicted in Figure11. When considering an in vitro environment where SULT and PAPS are incubated together prior to the addition of substrate, the dimer is free to bind either one or two molecules of PAPS depending on the concentration (Panel B or D). In either case, upon addition of substrate, a single subunit of the half-site reactive enzyme catalyzes sulfuryl transfer, forming PAP (Panel C or E). The enzyme is now free for PAPS to bind the neighboring subunit (Panel E). As illustrated in simulation [6], bound PAPS may stimulate an increase in Loop 3 flexibility in the PAP bound chain, favoring release of PAP, reestablishing a dimer complex with only one subunit bound to PAPS (panel B). This binding and release pattern can progress, oscillating between three distinct states, panels B, C, and E (Fig.11).

Bottom Line: While SULT dimerization is highly conserved, the necessity for the interaction has not been established.The results suggest the dimer subunits may possess the capability of communicating with one another in a manner dependent on the presence of the cofactor.These results suggest SULT dimerization may be important in maintaining cofactor binding/release properties of SULTs and provide hypothetical explanations for SULT half-site reactivity and substrate inhibition, which can be analyzed in vitro.

View Article: PubMed Central - PubMed

Affiliation: The Department of Pharmacology and Toxicology, The University of Alabama at Birmingham Birmingham, Alabama, 35294-0019.

ABSTRACT
The cytosolic sulfotransferases (SULTs) are dimeric enzymes that catalyze the transformation of hydrophobic drugs and hormones into hydrophilic sulfate esters thereby providing the body with an important pathway for regulating small molecule activity and excretion. While SULT dimerization is highly conserved, the necessity for the interaction has not been established. To perform its function, a SULT must efficiently bind the universal sulfate donor, 3'-phosphoadenosine-5'-phosphosulfate (PAPS), and release the byproduct, 3', 5'-diphosphoadenosine (PAP), following catalysis. We hypothesize this efficient binding and release of PAPS/PAP may be connected to SULT dimerization. To allow for the visualization of dynamic protein interactions critical for addressing this hypothesis and to generate kinetically testable hypotheses, molecular dynamic simulations (MDS) of hSULT1B1 were performed with PAPS and PAP bound to each dimer subunit in various combinations. The results suggest the dimer subunits may possess the capability of communicating with one another in a manner dependent on the presence of the cofactor. PAP or PAPS binding to a single side of the dimer results in decreased backbone flexibility of both the bound and unbound subunits, implying the dimer subunits may not act independently. Further, binding of PAP to one subunit of the dimer and PAPS to the other caused increased flexibility in the subunit bound to the inactive cofactor (PAP). These results suggest SULT dimerization may be important in maintaining cofactor binding/release properties of SULTs and provide hypothetical explanations for SULT half-site reactivity and substrate inhibition, which can be analyzed in vitro.

No MeSH data available.


Related in: MedlinePlus