A new allosteric site in glycogen phosphorylase b as a target for drug interactions

Oikonomakos, Nikos G.; Skamnaki, V.T.; Tsitsanou, Katerina E.; Gavalas, Nikos G.; Johnson, L.N.

doi:10.1016/s0969-2126(00)00144-1

Cited by 124 publications

(93 citation statements)

References 41 publications

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“…Glycogen-binding sites are 67 (minor site) to 94% (major site) conserved. A new allosteric (indole inhibitor) site was identified in the human liver and rabbit skeletal muscle isozymes (52,54). The amino acid sequence of this site is also identical in rat and human enzymes (29).…”

Section: Discussionmentioning

confidence: 96%

Integrated effects of multiple modulators on human liver glycogen phosphorylasea

Ercan-Fang

Gannon

Rath

et al. 2002

American Journal of Physiology-Endocrinology and Metabolism

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Hepatic glucose production is increased in people with type 2 diabetes. Glucose released from storage in liver glycogen by phosphorylase accounts for ϳ50% of the glucose produced after an overnight fast. Therefore, understanding how glycogenolysis in the liver is regulated is of great importance. Toward this goal, we have determined the kinetic characteristics of recombinant human liver glycogen phosphorylase a (HLGPa) (active form) and compared them with those of the purified rat enzyme (RLGPa). The Michaelis-Menten constant (K m) of HLGPa for Pi, 5 mM, was about fivefold greater than the Km of RLGPa. Two Pi (substrate) concentrations were used (1 and 5 mM) to cover the physiological range for P i. Other effectors were added at estimated intracellular concentrations. When added individually, AMP stimulated, whereas ADP, ATP and glucose inhibited, activity. These results were similar to those of the RLGPa. However, glucose inhibition was about twofold more potent with the human enzyme. UDP-glucose, glucose 6-phosphate, and fructose 1-phosphate were only minor inhibitors of both enzymes. We reported previously that when all known effectors were present in combination at physiological concentrations, the net effect was no change in RLGPa activity. However, the same combination reduced HLGPa activity, and the inhibition was glucose dependent. We conclude that a combination of the known effectors of phosphorylase a activity, when present at estimated intracellular concentrations, is inhibitory. Of these effectors, only glucose changes greatly in vivo. Thus it may be the major regulator of HLGPa activity. glucose; glycogen metabolism; enzyme regulation; adenosine 5Ј-monophosphate; adenosine 5Ј-diphosphate; adenosine 5Ј-triphosphate; glucose 1-phosphate; fructose 1-phosphate; uridine 5Ј-diphosphate-glucose IN HUMANS, GLUCOSE RELEASED from liver glycogen by the enzyme phosphorylase accounts for ϳ50% of the total glucose produced after an overnight fast, significantly contributing to the maintenance of a normal blood glucose concentration (11,27,38,53,63). Despite increased serum glucose level in people with type 2 diabetes, phosphorylase-mediated glycogenolysis continues to contribute ϳ40-50% of overnight glucose production, inappropriately maintaining hyperglycemia (3,4,21,63, 68). Once glycogenolysis decreases, as with extended fasting, the blood glucose concentration decreases dramatically (3,20,24,32, 68). Therefore, understanding how phosphorylase-mediated glycogenolysis is regulated in people with or without diabetes is of considerable importance.Phosphorylase removes glycosyl units from the terminal branches of glycogen through phosphorolysis, forming glucose 1-phosphate. It is present in two interconvertible forms, phosphorylase a (phosphorylated) and b (unphosphorylated). The a form is the active form. Regulation of phosphorylase is incompletely understood. Phosphorylase has been postulated to be primarily regulated by the interconversion of the active, phosphorylated (phosphorylase a) and inactive, nonphospho...

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Section: Discussionmentioning

confidence: 96%

Integrated effects of multiple modulators on human liver glycogen phosphorylasea

Ercan-Fang

Gannon

Rath

et al. 2002

American Journal of Physiology-Endocrinology and Metabolism

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“…On the protein surface, a total of 249 Å 2 solvent-accessible surface area becomes inaccessible on binding flavopiridol, of which 184 Å 2 (74%) is contributed by nonpolar groups. Bigger buried surfaces have been reported for other potent GP inhibitors such as W1807 (21) and CP320626 (24). The corresponding values for ligand and protein buried areas in the GPb⅐W1807 and GPb⅐CP320626 complexes are 518 Å 2 and 334 Å 2 (W1807; K i ϭ 1.6 nM), and 536 Å 2 and 283 Å 2 (CP320626; IC 50 ϭ 334 nM), respectively.…”

Section: Interactions Of Flavopiridol With Inhibitor Site Residues-mentioning

confidence: 86%

“…The inhibitor site, which binds purine compounds, such as caffeine, nucleosides, or nucleotides at high concentrations and flavopiridol (shown) is located on the surface of the enzyme some 12 Å from the catalytic site and, in the T state, obstructs the entrance to the catalytic site tunnel. The new allosteric inhibitor site (24), located inside the central cavity formed on association of the two subunits, binds CP320626 molecule (shown) and is some 15 Å from the allosteric effector site, 33 Å from the catalytic site and 37 Å from the the inhibitor site. these conditions, the mixtures were filtered out to remove precipitates.…”

Section: Crystallographic Experimentsmentioning

confidence: 99%

Flavopiridol Inhibits Glycogen Phosphorylase by Binding at the Inhibitor Site

Oikonomakos¹,

Schnier²,

Zographos³

et al. 2000

Journal of Biological Chemistry

124

111

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“…For example, the binding site for 5-chloro-1H-indole-2-carboxylic acid (1-(4-fluorobenzyl)-2-(4-hydroxypiperidin-1-yl)-2-oxoethyl)amide (CP320626) for glycogen phosphorylase b is 33 Å from the catalytic site and 15 Å from the site for cyclic AMP (Oikonomakos et al, 2000). If it is accepted that a direct connection (i.e., "hot wire") between the sites need not exist, then there is no limitation as to the distance between energetically linked allosteric and active sites on receptors.…”

mentioning

confidence: 99%

Seven Transmembrane Receptors as Shapeshifting Proteins: The Impact of Allosteric Modulation and Functional Selectivity on New Drug Discovery

2010

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A new allosteric site in glycogen phosphorylase b as a target for drug interactions

Cited by 124 publications

References 41 publications

Integrated effects of multiple modulators on human liver glycogen phosphorylasea

Integrated effects of multiple modulators on human liver glycogen phosphorylasea

Flavopiridol Inhibits Glycogen Phosphorylase by Binding at the Inhibitor Site

Seven Transmembrane Receptors as Shapeshifting Proteins: The Impact of Allosteric Modulation and Functional Selectivity on New Drug Discovery

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