2gpa
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ALLOSTERIC INHIBITION OF GLYCOGEN PHOSPHORYLASE A BY A POTENTIAL ANTIDIABETIC DRUG
OverviewOverview
The effect of the potential antidiabetic drug (-)(S)-3-isopropyl, 4-(2-chlorophenyl)-1,4-dihydro-1-ethyl-2-methyl-pyridine-3,5,6-tricarbox, ylate (W1807) on the catalytic and structural properties of glycogen, phosphorylase a has been studied. Glycogen phosphorylase (GP) is an, allosteric enzyme whose activity is primarily controlled by reversible, phosphorylation of Ser14 of the dephosphorylated enzyme (GPb, less active, predominantly T-state) to form the phosphorylated enzyme (GPa, more, active, predominantly R-state). Upon conversion of GPb to GPa, the, N-terminal tail (residues 5-22), which carries the Ser14(P), changes its, conformation into a distorted 3(10) helix and its contacts from, intrasubunit to intersubunit. This alteration causes a series of tertiary, and quaternary conformational changes that lead to activation of the, enzyme through opening access to the catalytic site. As part of a, screening process to identify compounds that might contribute to the, regulation of glycogen metabolism in the noninsulin dependent diabetes, diseased state, W1807 has been found as the most potent inhibitor of GPb, (Ki = 1.6 nM) that binds at the allosteric site of T-state GPb and, produces further conformational changes, characteristic of a T'-like, state. Kinetics show W1807 is a potent competitive inhibitor of GPa (-AMP), (Ki = 10.8 nM) and of GPa (+1 mM AMP) (Ki = 19.4 microM) with respect to, glucose 1-phosphate and acts in synergism with glucose. To elucidate the, structural features that contribute to the binding, the structures of GPa, in the T-state conformation in complex with glucose and in complex with, both glucose and W1807 have been determined at 100 K to 2.0 A and 2.1 A, resolution, and refined to crystallographic R-values of 0.179 (R(free) =, 0.230) and 0.189 (R(free) = 0.263), respectively. W1807 binds tightly at, the allosteric site and induces substantial conformational changes both in, the vicinity of the allosteric site and the subunit interface. A, disordering of the N-terminal tail occurs, while the loop of chain, containing residues 192-196 and residues 43'-49' shift to accommodate the, ligand. Structural comparisons show that the T-state GPa-glucose-W1807, structure is overall more similar to the T-state GPb-W1807 complex, structure than to the GPa-glucose complex structure, indicating that W1807, is able to transform GPa to the T'-like state already observed with GPb., The structures provide a rational for the potency of the inhibitor and, explain GPa allosteric inhibition of activity upon W1807 binding.
About this StructureAbout this Structure
2GPA is a Single protein structure of sequence from Oryctolagus cuniculus with GLC, PO3, PLP and GOL as ligands. Active as Phosphorylase, with EC number 2.4.1.1 Full crystallographic information is available from OCA.
ReferenceReference
Allosteric inhibition of glycogen phosphorylase a by the potential antidiabetic drug 3-isopropyl 4-(2-chlorophenyl)-1,4-dihydro-1-ethyl-2-methyl-pyridine-3,5,6-tricarbo xylate., Oikonomakos NG, Tsitsanou KE, Zographos SE, Skamnaki VT, Goldmann S, Bischoff H, Protein Sci. 1999 Oct;8(10):1930-45. PMID:10548038
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