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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

Effects of PAPS/PAP-binding on the mobility (RMSF) of amino acids 208–273, including Loop 3 (aa 235–268) and a portion of the dimerization domain (aa 266–275). (A) Subunit A of simulations [1], [2], and [3]. (B) Subunit B of simulations [1], [2], and [3]. A relatively high level of stability was observed for residue 250 across simulations (trough indicated by black arrow). The key indicates the PAP/PAPS-binding state of each subunit. A secondary structure map of the highlighted region is available toward the bottom of the graph (L3 = Loop 3, green cylinders = α-helix).
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fig05: Effects of PAPS/PAP-binding on the mobility (RMSF) of amino acids 208–273, including Loop 3 (aa 235–268) and a portion of the dimerization domain (aa 266–275). (A) Subunit A of simulations [1], [2], and [3]. (B) Subunit B of simulations [1], [2], and [3]. A relatively high level of stability was observed for residue 250 across simulations (trough indicated by black arrow). The key indicates the PAP/PAPS-binding state of each subunit. A secondary structure map of the highlighted region is available toward the bottom of the graph (L3 = Loop 3, green cylinders = α-helix).

Mentions: The change in the average RMSF values for each chain is most likely the result of a change in the dynamics of specific portions of the protein. Therefore, the relative mobility of each residue along the backbone of the protein was compared. Specific regions of the protein showed significant alterations in response to PAP or PAPS binding. One of these regions was Loop 3. Figure5 depicts the mobility of Loop 3 (aa 235–263) in simulations [1], [2], and [3]. Direct comparison of subunit A from each simulation shows the presence of either PAP or PAPS decreases the flexibility of Loop 3 in the vicinity of residue 262, directly adjacent to the KTVE dimerization domain. It exhibits an RMSF of 3.07 Å in the apo enzyme (simulation [1]), while the presence of PAPS or PAP reduces this RMSF value to 0.6 and 1.75 Å, respectively (simulations [2] and [3]). Regardless of the presence of the cofactor, relative flexibility, represented by a trough in the RMSF line, was observed at residue 250 (Asp) across all simulations (Fig.5A and B). This trough separates Loop 3 into two halves; the N-terminal half overlaying the substrate binding domain and the C-terminal half overlaying the PAPS binding domain. In subunit B in simulations [1], [2], and [3] (all of which are in an apo state), residue 262 exhibited similar mobility. The N-terminal half of Loop 3 is highly mobile in chain B of simulation [1], while it is stable in simulations [2] and [3].


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

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

Effects of PAPS/PAP-binding on the mobility (RMSF) of amino acids 208–273, including Loop 3 (aa 235–268) and a portion of the dimerization domain (aa 266–275). (A) Subunit A of simulations [1], [2], and [3]. (B) Subunit B of simulations [1], [2], and [3]. A relatively high level of stability was observed for residue 250 across simulations (trough indicated by black arrow). The key indicates the PAP/PAPS-binding state of each subunit. A secondary structure map of the highlighted region is available toward the bottom of the graph (L3 = Loop 3, green cylinders = α-helix).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig05: Effects of PAPS/PAP-binding on the mobility (RMSF) of amino acids 208–273, including Loop 3 (aa 235–268) and a portion of the dimerization domain (aa 266–275). (A) Subunit A of simulations [1], [2], and [3]. (B) Subunit B of simulations [1], [2], and [3]. A relatively high level of stability was observed for residue 250 across simulations (trough indicated by black arrow). The key indicates the PAP/PAPS-binding state of each subunit. A secondary structure map of the highlighted region is available toward the bottom of the graph (L3 = Loop 3, green cylinders = α-helix).
Mentions: The change in the average RMSF values for each chain is most likely the result of a change in the dynamics of specific portions of the protein. Therefore, the relative mobility of each residue along the backbone of the protein was compared. Specific regions of the protein showed significant alterations in response to PAP or PAPS binding. One of these regions was Loop 3. Figure5 depicts the mobility of Loop 3 (aa 235–263) in simulations [1], [2], and [3]. Direct comparison of subunit A from each simulation shows the presence of either PAP or PAPS decreases the flexibility of Loop 3 in the vicinity of residue 262, directly adjacent to the KTVE dimerization domain. It exhibits an RMSF of 3.07 Å in the apo enzyme (simulation [1]), while the presence of PAPS or PAP reduces this RMSF value to 0.6 and 1.75 Å, respectively (simulations [2] and [3]). Regardless of the presence of the cofactor, relative flexibility, represented by a trough in the RMSF line, was observed at residue 250 (Asp) across all simulations (Fig.5A and B). This trough separates Loop 3 into two halves; the N-terminal half overlaying the substrate binding domain and the C-terminal half overlaying the PAPS binding domain. In subunit B in simulations [1], [2], and [3] (all of which are in an apo state), residue 262 exhibited similar mobility. The N-terminal half of Loop 3 is highly mobile in chain B of simulation [1], while it is stable in simulations [2] and [3].

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