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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

Average α-carbon RMSF values for both hSULT1B1 dimer subunits (A and B). The color of each bar represents binding state of the subunit: White = No cofactor, Black = PAPS, Grey = PAP.
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fig04: Average α-carbon RMSF values for both hSULT1B1 dimer subunits (A and B). The color of each bar represents binding state of the subunit: White = No cofactor, Black = PAPS, Grey = PAP.

Mentions: Following equilibration (Fig.3), the RMSF of each α-carbon atom (excluding the ten N- and C-terminal residues) was calculated. Average RMSF values for each subunit are reported in Figure4, providing a quantitative description of the overall flexibility of each hSULT1B1 subunit. Each subunit of the fully apo dimer displayed the highest average flexibility with RMSF values of 1.08 and 1.1 Å (subunits A and B, respectively). Binding of PAPS or PAP to a single chain of the dimer decreases the flexibility in both the bound subunit and its unbound partner (Fig.4). PAPS (0.82 Å) appears to decrease the protein flexibility more than PAP (0.90 Å). Saturation of both dimeric subunits with either PAPS or PAP further decreases the flexibility of the enzyme (PAPS Avg. 0.78 Å, PAP Avg. 0.81 Å). When each subunit of the dimer is differentially bound to PAPS and PAP, the PAPS-bound chain is in the most stable state (0.76 Å), while the partnering PAP-bound chain is significantly more unstable (1.04 Å).


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

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

Average α-carbon RMSF values for both hSULT1B1 dimer subunits (A and B). The color of each bar represents binding state of the subunit: White = No cofactor, Black = PAPS, Grey = PAP.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig04: Average α-carbon RMSF values for both hSULT1B1 dimer subunits (A and B). The color of each bar represents binding state of the subunit: White = No cofactor, Black = PAPS, Grey = PAP.
Mentions: Following equilibration (Fig.3), the RMSF of each α-carbon atom (excluding the ten N- and C-terminal residues) was calculated. Average RMSF values for each subunit are reported in Figure4, providing a quantitative description of the overall flexibility of each hSULT1B1 subunit. Each subunit of the fully apo dimer displayed the highest average flexibility with RMSF values of 1.08 and 1.1 Å (subunits A and B, respectively). Binding of PAPS or PAP to a single chain of the dimer decreases the flexibility in both the bound subunit and its unbound partner (Fig.4). PAPS (0.82 Å) appears to decrease the protein flexibility more than PAP (0.90 Å). Saturation of both dimeric subunits with either PAPS or PAP further decreases the flexibility of the enzyme (PAPS Avg. 0.78 Å, PAP Avg. 0.81 Å). When each subunit of the dimer is differentially bound to PAPS and PAP, the PAPS-bound chain is in the most stable state (0.76 Å), while the partnering PAP-bound chain is significantly more unstable (1.04 Å).

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