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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

Comparison of the mobility (RMSF) of each subunit B residue in three simulations ([4], [5], and [6]). As illustrated in the key, orange and teal both indicate a chain bound with PAP – the partnering chain of each is bound with PAP and PAPS, respectively. Purple indicates a PAPS-bound chain partnered with another PAPS-bound chain. A secondary structure map of the highlighted region is available toward the bottom of the graph (green cylinders = α-helix, magenta arrows = β-sheet backbone, L1/2/3 = Loops 1/2/3).
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fig06: Comparison of the mobility (RMSF) of each subunit B residue in three simulations ([4], [5], and [6]). As illustrated in the key, orange and teal both indicate a chain bound with PAP – the partnering chain of each is bound with PAP and PAPS, respectively. Purple indicates a PAPS-bound chain partnered with another PAPS-bound chain. A secondary structure map of the highlighted region is available toward the bottom of the graph (green cylinders = α-helix, magenta arrows = β-sheet backbone, L1/2/3 = Loops 1/2/3).

Mentions: Figure6 depicts the complete RMSF of subunit B when the dimeric enzyme is fully saturated with cofactor (either PAP or PAPS). This figure shows that Loop 3 is highly mobile (approximately 3.9 Å) for chain B in simulation [6] relative to simulations [4] and [5]. A second region, upstream of Loop 1 (aa 63-72), is also more mobile throughout this simulation relative to the control simulations. The increased mobility of these two regions is the largest contributor to the general flexibility of this chain depicted in Figure4. The outlier (chain B of simulation [6]) is PAP-bound but is paired with a partnering subunit that is PAPS-bound while both chains of hSULT1B1 are saturated with PAPS and PAP in simulations [4] and [5], respectively. The following analyses were designed to further understand the cause of the flexibility to these particular regions of hSULT1B1 to evaluate its potential involvement in the hSULT1B1 mechanism.


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

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

Comparison of the mobility (RMSF) of each subunit B residue in three simulations ([4], [5], and [6]). As illustrated in the key, orange and teal both indicate a chain bound with PAP – the partnering chain of each is bound with PAP and PAPS, respectively. Purple indicates a PAPS-bound chain partnered with another PAPS-bound chain. A secondary structure map of the highlighted region is available toward the bottom of the graph (green cylinders = α-helix, magenta arrows = β-sheet backbone, L1/2/3 = Loops 1/2/3).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig06: Comparison of the mobility (RMSF) of each subunit B residue in three simulations ([4], [5], and [6]). As illustrated in the key, orange and teal both indicate a chain bound with PAP – the partnering chain of each is bound with PAP and PAPS, respectively. Purple indicates a PAPS-bound chain partnered with another PAPS-bound chain. A secondary structure map of the highlighted region is available toward the bottom of the graph (green cylinders = α-helix, magenta arrows = β-sheet backbone, L1/2/3 = Loops 1/2/3).
Mentions: Figure6 depicts the complete RMSF of subunit B when the dimeric enzyme is fully saturated with cofactor (either PAP or PAPS). This figure shows that Loop 3 is highly mobile (approximately 3.9 Å) for chain B in simulation [6] relative to simulations [4] and [5]. A second region, upstream of Loop 1 (aa 63-72), is also more mobile throughout this simulation relative to the control simulations. The increased mobility of these two regions is the largest contributor to the general flexibility of this chain depicted in Figure4. The outlier (chain B of simulation [6]) is PAP-bound but is paired with a partnering subunit that is PAPS-bound while both chains of hSULT1B1 are saturated with PAPS and PAP in simulations [4] and [5], respectively. The following analyses were designed to further understand the cause of the flexibility to these particular regions of hSULT1B1 to evaluate its potential involvement in the hSULT1B1 mechanism.

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