Assay methods for identifying glycogen synthase kinase 3 modulators
Methods and compositions for glycogen synthase kinase 3 assays continue to be required for detection of glycogen synthase 3 kinase, assessment of glycogen synthase 3 kinase activity and identification of modulators of glycogen synthase 3 kinase. Methods and compositions for glycogen synthase kinase 3 assays are provided herein based on the discovery of a previously unknown interaction between glycogen synthase 3 kinase and eukaryotic translation initiation factor 4E-binding protein 1 which serves as a substrate for glycogen synthase kinase 3-alpha and glycogen synthase kinase 3-beta.
1. An in vitro method of identifying a glycogen synthase kinase 3 (GSK3) modulator, comprising contacting a GSK3 and a 4E-BP1-derived GSK3 substrate under GSK3 kinase activity reaction conditions, in the presence and absence of a test substance;
wherein the GSK3 comprises a protein selected from the group consisting of:
(i) the GSK3 of SEQ ID No: 1 or 3,
(ii) a protein consisting of a sequence at least 95% identical to SEQ ID NO: 1 or 3 and functional to phosphorylate SEQ ID NO: 5, on residues Thr 37 and/or Thr 46 , and
(iii) a GSK3 encoded by the complement of a nucleic acid which hybridizes to SEQ ID No: 2 or 4 under highly stringent hybridization conditions comprising hybridization in a solution containing 6×SSC, 5× Denhardt's solution, 30% formamide, and 100 micrograms/ml denatured salmon sperm at 37° C. overnight, followed by washing in a solution of 0.1×SSC and 0.1% SDS at 65° C. for 15 minutes and functional to phosphorylate SEQ ID NO: 5, on residues Thr 37 and/or Thr 46 ;
wherein the 4E-BP1-derived GSK3 substrate comprises a non-primed protein selected from the group consisting of:
(a) the polypeptide of SEQ ID No. 5,
(b) a polypeptide consisting of a sequence at least 90% identical to SEQ ID NO: 5 and having at least one Thr-X-X-X-Thr motif, where each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3,
(c) the polypeptide of SEQ ID No. 7,
(d) a polypeptide consisting of a sequence at least 90% identical to SEQ ID NO: 7 and having at least one Thr-X-X-X-Thr motif, where each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3,
(e) the polypeptide of SEQ ID No. 8,
(f) a polypeptide consisting of a sequence at least 90% identical to SEQ ID NO: 8 and having at least one Thr-X-X-X-Thr motif, where each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3,
(g) a polypeptide consisting of a sequence encoded by the complement of a nucleic acid which hybridizes to SEQ ID No: 6 under highly stringent hybridization conditions comprising hybridization in a solution containing 6×SSC, 5× Denhardt's solution, 30% formamide, and 100 micrograms/ml denatured salmon sperm at 37° C. overnight, followed by washing in a solution of 0.1×SSC and 0.1% SDS at 65° C. for 15 minutes, said polypeptide having at least one motif, Thr-X-X-X-Thr, where each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3, and
(h) a fragment of a polypeptide consisting of a sequence at least 90% identical to SEQ ID NO: 5 and having at least one Thr-X-X-X-Thr motif, where each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3;
wherein the method detects phosphorylation of the 4E-BP1-derived GSK3 substrate by the GSK3 polypeptide and;
wherein changes in the phosphorylation of the 4E-BP1-derived GSK3 substrate by the GSK3 polypeptide in the presence, compared to the absence, of the test substance identifies the test substance as a GSK3 modulator.
2. The method of identifying a GSK3 modulator of claim 1 , wherein the GSK3 comprises a protein having at least 96% identity to SEQ ID NO: 1 or SEQ ID NO:3 and the protein is functional to phosphorylate SEQ ID NO: 5, on residues Thr 37 and/or Thr 46 .
3. The method of identifying a GSK3 modulator of claim 1 , wherein the 4E-BP 1-derived GSK3 substrate comprises a protein having at least 91%, identity to SEQ ID NO: 5, SEQ ID NO: 7, or SEQ ID NO: 8 and having at least one GSK3 phosphorylation motif Thr-X-X-X-Thr, wherein each X is an independently selected amino acid, and each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3.
4. The method of identifying a GSK3 modulator of claim 1 , wherein the 4E-BP1-derived GSK3 substrate comprises a variant of a fragment of SEQ ID No. 5, wherein said variant fragment has at least 10 amino acids, has at least 91% to the corresponding fragment of SEQ ID NO: 5, includes at least one Thr-X-X-X-Thr motif, wherein each X is an independently selected amino acid, and wherein each of said at least one motif can be phosphorylated by the protein of SEQ ID NO: 1 or 3.