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3'-Phosphoadenosine 5'-phosphosulfate allosterically regulates sulfotransferase turnover.

Wang T, Cook I, Leyh TS - Biochemistry (2014)

Bottom Line: The first nucleotide to bind causes closure of the cap to which it is bound and at the same time stabilizes the cap in the adjacent subunit in the open position.Cap closure sterically controls active-site access of the nucleotide and acceptor; consequently, the structural changes in the cap that occur as a function of nucleotide occupancy lead to changes in the substrate affinities and turnover of the enzyme.PAPS levels in tissues from a variety of organs suggest that the catalytic efficiency of the enzyme varies across tissues over the full 130-fold range and that efficiency is greatest in those tissues that experience the greatest xenobiotic "load".

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461-1926, United States.

ABSTRACT
Human cytosolic sulfotransferases (SULTs) regulate the activities of thousands of small molecules-metabolites, drugs, and other xenobiotics-via the transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the hydroxyls and primary amines of acceptors. SULT1A1 is the most abundant SULT in liver and has the broadest substrate spectrum of any SULT. Here we present the discovery of a new form of SULT1A1 allosteric regulation that modulates the catalytic efficiency of the enzyme over a 130-fold dynamic range. The molecular basis of the regulation is explored in detail and is shown to be rooted in an energetic coupling between the active-site caps of adjacent subunits in the SULT1A1 dimer. The first nucleotide to bind causes closure of the cap to which it is bound and at the same time stabilizes the cap in the adjacent subunit in the open position. Binding of the second nucleotide causes both caps to open. Cap closure sterically controls active-site access of the nucleotide and acceptor; consequently, the structural changes in the cap that occur as a function of nucleotide occupancy lead to changes in the substrate affinities and turnover of the enzyme. PAPS levels in tissues from a variety of organs suggest that the catalytic efficiency of the enzyme varies across tissues over the full 130-fold range and that efficiency is greatest in those tissues that experience the greatest xenobiotic "load".

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Coupling of PAPS binding and cap closure in SULT1A1. Theligandbinding sites of the unliganded enzyme are open and can receive ligands.Binding of the first PAPS molecule closes both the PAPS and acceptorbinding sites of the subunit to which PAPS has bound. In this configuration,PAPS cannot escape and only small acceptors can enter unless the enzymeisomerizes to the open form (not shown), which is unfavorable (Kiso = 26 in favor of the closed state). Consequently,the singly PAPS-bound configuration favors small acceptors. As thesecond PAPS molecule binds, all of the binding sites open, thus alleviatingthe catalytic bias against large substrates, and each subunit turnsover 4-fold faster.
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fig7: Coupling of PAPS binding and cap closure in SULT1A1. Theligandbinding sites of the unliganded enzyme are open and can receive ligands.Binding of the first PAPS molecule closes both the PAPS and acceptorbinding sites of the subunit to which PAPS has bound. In this configuration,PAPS cannot escape and only small acceptors can enter unless the enzymeisomerizes to the open form (not shown), which is unfavorable (Kiso = 26 in favor of the closed state). Consequently,the singly PAPS-bound configuration favors small acceptors. As thesecond PAPS molecule binds, all of the binding sites open, thus alleviatingthe catalytic bias against large substrates, and each subunit turnsover 4-fold faster.

Mentions: PAPS binds antisynergistically to the subunits of the SULT1A1 dimer.Nucleotide binding at the first subunit causes an 81-fold weakeningin the affinity at the second. The decreased affinity is due solelyto an increase in the nucleotide off rate constant, which stronglysuggests that the cap at the weak affinity site is stabilized in theopen position. To determine the cap configurations at all four ligandbinding sites as a function of PAPS occupancy, cap positioning atthe acceptor pockets was determined using large and small acceptors.PAPS binding at the first site closes both the nucleotide and acceptorcap segments only on the subunit to which PAPS is bound; the cap onthe adjacent subunit remains open at both sites. Once the second nucleotideadds, the caps open at all four ligand binding pockets. The couplingof PAPS binding and cap closure is depicted in Figure 7. In this configuration, kcat isincreased 8-fold relative to that of the singly PAPS-bound enzyme,and Km decreases 23-fold toward largesubstrates. Finally, estimates of PAPS concentrations across a varietyof tissues suggest that SULT1A1 reactivity will be highly tissue-dependent,and that the enzyme will function in its broadest specificity andhighest turnover mode in tissues that experience the highest levelsof xenobiotics.


3'-Phosphoadenosine 5'-phosphosulfate allosterically regulates sulfotransferase turnover.

Wang T, Cook I, Leyh TS - Biochemistry (2014)

Coupling of PAPS binding and cap closure in SULT1A1. Theligandbinding sites of the unliganded enzyme are open and can receive ligands.Binding of the first PAPS molecule closes both the PAPS and acceptorbinding sites of the subunit to which PAPS has bound. In this configuration,PAPS cannot escape and only small acceptors can enter unless the enzymeisomerizes to the open form (not shown), which is unfavorable (Kiso = 26 in favor of the closed state). Consequently,the singly PAPS-bound configuration favors small acceptors. As thesecond PAPS molecule binds, all of the binding sites open, thus alleviatingthe catalytic bias against large substrates, and each subunit turnsover 4-fold faster.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230322&req=5

fig7: Coupling of PAPS binding and cap closure in SULT1A1. Theligandbinding sites of the unliganded enzyme are open and can receive ligands.Binding of the first PAPS molecule closes both the PAPS and acceptorbinding sites of the subunit to which PAPS has bound. In this configuration,PAPS cannot escape and only small acceptors can enter unless the enzymeisomerizes to the open form (not shown), which is unfavorable (Kiso = 26 in favor of the closed state). Consequently,the singly PAPS-bound configuration favors small acceptors. As thesecond PAPS molecule binds, all of the binding sites open, thus alleviatingthe catalytic bias against large substrates, and each subunit turnsover 4-fold faster.
Mentions: PAPS binds antisynergistically to the subunits of the SULT1A1 dimer.Nucleotide binding at the first subunit causes an 81-fold weakeningin the affinity at the second. The decreased affinity is due solelyto an increase in the nucleotide off rate constant, which stronglysuggests that the cap at the weak affinity site is stabilized in theopen position. To determine the cap configurations at all four ligandbinding sites as a function of PAPS occupancy, cap positioning atthe acceptor pockets was determined using large and small acceptors.PAPS binding at the first site closes both the nucleotide and acceptorcap segments only on the subunit to which PAPS is bound; the cap onthe adjacent subunit remains open at both sites. Once the second nucleotideadds, the caps open at all four ligand binding pockets. The couplingof PAPS binding and cap closure is depicted in Figure 7. In this configuration, kcat isincreased 8-fold relative to that of the singly PAPS-bound enzyme,and Km decreases 23-fold toward largesubstrates. Finally, estimates of PAPS concentrations across a varietyof tissues suggest that SULT1A1 reactivity will be highly tissue-dependent,and that the enzyme will function in its broadest specificity andhighest turnover mode in tissues that experience the highest levelsof xenobiotics.

Bottom Line: The first nucleotide to bind causes closure of the cap to which it is bound and at the same time stabilizes the cap in the adjacent subunit in the open position.Cap closure sterically controls active-site access of the nucleotide and acceptor; consequently, the structural changes in the cap that occur as a function of nucleotide occupancy lead to changes in the substrate affinities and turnover of the enzyme.PAPS levels in tissues from a variety of organs suggest that the catalytic efficiency of the enzyme varies across tissues over the full 130-fold range and that efficiency is greatest in those tissues that experience the greatest xenobiotic "load".

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461-1926, United States.

ABSTRACT
Human cytosolic sulfotransferases (SULTs) regulate the activities of thousands of small molecules-metabolites, drugs, and other xenobiotics-via the transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the hydroxyls and primary amines of acceptors. SULT1A1 is the most abundant SULT in liver and has the broadest substrate spectrum of any SULT. Here we present the discovery of a new form of SULT1A1 allosteric regulation that modulates the catalytic efficiency of the enzyme over a 130-fold dynamic range. The molecular basis of the regulation is explored in detail and is shown to be rooted in an energetic coupling between the active-site caps of adjacent subunits in the SULT1A1 dimer. The first nucleotide to bind causes closure of the cap to which it is bound and at the same time stabilizes the cap in the adjacent subunit in the open position. Binding of the second nucleotide causes both caps to open. Cap closure sterically controls active-site access of the nucleotide and acceptor; consequently, the structural changes in the cap that occur as a function of nucleotide occupancy lead to changes in the substrate affinities and turnover of the enzyme. PAPS levels in tissues from a variety of organs suggest that the catalytic efficiency of the enzyme varies across tissues over the full 130-fold range and that efficiency is greatest in those tissues that experience the greatest xenobiotic "load".

Show MeSH
Related in: MedlinePlus