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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

Observational shifts in hSULT1B1 structure. Loop 1 (aa 85-92), a region upstream of Loop 1 (aa 63-72), and Loop 3 show the most variability throughout the different simulations. PAP (teal spheres) is present for reference and orientation. A key β-bridge (blue dash) is lost in chain B of simulation [6] (green cartoon), but is present in chain B of simulation [5] (magenta cartoon) as well as all other simulations, resulting in high mobility of Loop 3.
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fig07: Observational shifts in hSULT1B1 structure. Loop 1 (aa 85-92), a region upstream of Loop 1 (aa 63-72), and Loop 3 show the most variability throughout the different simulations. PAP (teal spheres) is present for reference and orientation. A key β-bridge (blue dash) is lost in chain B of simulation [6] (green cartoon), but is present in chain B of simulation [5] (magenta cartoon) as well as all other simulations, resulting in high mobility of Loop 3.

Mentions: Selection of individual frames for analysis could bias results, therefore, average protein structures over the last 10 nsec of simulation were compared. Figure7 shows the structural alterations that are primarily responsible for the observed RMSF alterations in chain B of simulation [6]. A critical β-bridge between Loop 3 and the base of the active site (Met146 and Asp250) is intact in chain B of simulations [4] (not shown) and [5], but appears to be nonexistent in chain B of simulation [6]. Residues 63-72 adopt an α-helical conformation in simulations [4] (not shown) and [5], but this region is unstructured in chain B of simulation [6] (Fig.7). Loop 1 adopts a similar conformation in all three simulations (Fig.7) and displays similar mobility in each simulation (Fig.6).


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

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

Observational shifts in hSULT1B1 structure. Loop 1 (aa 85-92), a region upstream of Loop 1 (aa 63-72), and Loop 3 show the most variability throughout the different simulations. PAP (teal spheres) is present for reference and orientation. A key β-bridge (blue dash) is lost in chain B of simulation [6] (green cartoon), but is present in chain B of simulation [5] (magenta cartoon) as well as all other simulations, resulting in high mobility of Loop 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig07: Observational shifts in hSULT1B1 structure. Loop 1 (aa 85-92), a region upstream of Loop 1 (aa 63-72), and Loop 3 show the most variability throughout the different simulations. PAP (teal spheres) is present for reference and orientation. A key β-bridge (blue dash) is lost in chain B of simulation [6] (green cartoon), but is present in chain B of simulation [5] (magenta cartoon) as well as all other simulations, resulting in high mobility of Loop 3.
Mentions: Selection of individual frames for analysis could bias results, therefore, average protein structures over the last 10 nsec of simulation were compared. Figure7 shows the structural alterations that are primarily responsible for the observed RMSF alterations in chain B of simulation [6]. A critical β-bridge between Loop 3 and the base of the active site (Met146 and Asp250) is intact in chain B of simulations [4] (not shown) and [5], but appears to be nonexistent in chain B of simulation [6]. Residues 63-72 adopt an α-helical conformation in simulations [4] (not shown) and [5], but this region is unstructured in chain B of simulation [6] (Fig.7). Loop 1 adopts a similar conformation in all three simulations (Fig.7) and displays similar mobility in each simulation (Fig.6).

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