Limits...
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

The relative locations of the dimerization domain and substrate-binding domains of SULTs. A cartoon illustration shows the PAPS-binding domain (green) of each dimer subunit (A and B) is near the dimer interface, with key residues KxxxTVxxxE forming antiparallel interactions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4492763&req=5

fig01: The relative locations of the dimerization domain and substrate-binding domains of SULTs. A cartoon illustration shows the PAPS-binding domain (green) of each dimer subunit (A and B) is near the dimer interface, with key residues KxxxTVxxxE forming antiparallel interactions.

Mentions: Each human SULT isoform is a physiological homodimer whether or not it is bound to a ligand (Petrotchenko et al. 2001; Rehse et al. 2002; Weitzner et al. 2009). The two dimeric subunits interface in an antiparallel orientation along a small, highly conserved, motif near the C-terminus with the consensus amino acid sequence KxxxTVxxxE (Fig.1) (Petrotchenko et al. 2001; Pan et al. 2008; Weitzner et al. 2009). Despite the conservation of SULT dimerization, no suitable functional rationale for subunit oligomerization has been identified. The literature contains reports of monomeric SULTs (primarily generated via mutation) displaying altered substrate inhibition patterns and increased vulnerability to heat denaturation with minimal impact on sulfation activity (Lu et al. 2009; Cook et al. 2010a). Notably, three SULT isoforms (bovine SULT1A1, hSULT1E1, and hSULT2A1) have been described as exhibiting “half-site reactivity,” a phenomenon in which only half of the catalytic subunits catalyze the reaction at any given time (Beckmann et al. 2003; Sun and Leyh 2010; Wang et al. 2014). This phenomenon was first reported over 40 years ago and is a fairly common attribute of enzyme families including aldehyde dehydrogenases, thymidylate synthases, and biotin carboxylases (Matthews and Bernhard 1973; Anderson et al. 1999; Mochalkin et al. 2008; Yoval-Sanchez et al. 2013). To exhibit such a mechanism, the subunits of an oligomeric complex, like the SULT dimer, are required to “communicate” with one another in a coordinated fashion. The overall conservation and proximity of the dimerization domain to the PAPS-binding domain lend themselves to the hypothesis that the binding of PAPS, which is already known to elicit changes to SULT structure, may confer structural changes that are communicated to the neighboring subunit. A detailed description of this mechanism could provide an explanation for the preservation of human SULT dimerization as well as offer insight toward other SULT phenomena such as substrate inhibition.


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

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

The relative locations of the dimerization domain and substrate-binding domains of SULTs. A cartoon illustration shows the PAPS-binding domain (green) of each dimer subunit (A and B) is near the dimer interface, with key residues KxxxTVxxxE forming antiparallel interactions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig01: The relative locations of the dimerization domain and substrate-binding domains of SULTs. A cartoon illustration shows the PAPS-binding domain (green) of each dimer subunit (A and B) is near the dimer interface, with key residues KxxxTVxxxE forming antiparallel interactions.
Mentions: Each human SULT isoform is a physiological homodimer whether or not it is bound to a ligand (Petrotchenko et al. 2001; Rehse et al. 2002; Weitzner et al. 2009). The two dimeric subunits interface in an antiparallel orientation along a small, highly conserved, motif near the C-terminus with the consensus amino acid sequence KxxxTVxxxE (Fig.1) (Petrotchenko et al. 2001; Pan et al. 2008; Weitzner et al. 2009). Despite the conservation of SULT dimerization, no suitable functional rationale for subunit oligomerization has been identified. The literature contains reports of monomeric SULTs (primarily generated via mutation) displaying altered substrate inhibition patterns and increased vulnerability to heat denaturation with minimal impact on sulfation activity (Lu et al. 2009; Cook et al. 2010a). Notably, three SULT isoforms (bovine SULT1A1, hSULT1E1, and hSULT2A1) have been described as exhibiting “half-site reactivity,” a phenomenon in which only half of the catalytic subunits catalyze the reaction at any given time (Beckmann et al. 2003; Sun and Leyh 2010; Wang et al. 2014). This phenomenon was first reported over 40 years ago and is a fairly common attribute of enzyme families including aldehyde dehydrogenases, thymidylate synthases, and biotin carboxylases (Matthews and Bernhard 1973; Anderson et al. 1999; Mochalkin et al. 2008; Yoval-Sanchez et al. 2013). To exhibit such a mechanism, the subunits of an oligomeric complex, like the SULT dimer, are required to “communicate” with one another in a coordinated fashion. The overall conservation and proximity of the dimerization domain to the PAPS-binding domain lend themselves to the hypothesis that the binding of PAPS, which is already known to elicit changes to SULT structure, may confer structural changes that are communicated to the neighboring subunit. A detailed description of this mechanism could provide an explanation for the preservation of human SULT dimerization as well as offer insight toward other SULT phenomena such as substrate inhibition.

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