3-phosphoinositide-dependent protein kinase

1. A substantially pure human 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα at a rate substantially the same as the rate wildtype PDK1 activates protein kinase Bα, wherein the protein kinase comprises amino acids 83 to 342 and 450-550 of SEQ ID NO:1.

2. The substantially pure human 3-phosphoinositide-dependent protein kinase according to claim 1 , wherein the 3-phosphoinositide-dependent protein kinase has a molecular weight of about 67 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis.

3. A substantially pure 3-phosphoinositide dependent protein kinase having the amino acid sequence as shown in SEQ ID. NO:1 with from 1 to 4 conservative substitutions therein and wherein the protein kinase activates protein kinase Bα at a rate substantially the same as the rate wildtype PDK1 activates protein kinase Bα.

4. The substantially pure human 3-phosphoinositide-dependent protein kinase according to claim 1 wherein the 3-phosphoinositide-dependent protein kinase is a phosphatidylinositol-3,4,5-trisphosphate-dependent protein kinase.

5. The 3-phosphoinositide-dependent protein kinase according to claim 1 which activates protein kinase Bα in the presence of the D-enantiomer of Sn-1-stearoyl-2-arachidonyl phosphatidylinositol 3,4,5-trisphosphate but does not activate protein kinase Bα in the presence of the L-enantiomer of the said phosphatidylinositol 3,4,5-trisphosphate.

6. The 3-phosphoinositide-dependent protein kinase according to claim 1 which is activated by the D-enantiomer of sn-1,2-dipalmitoyl phosphatidylinositol 3,4,5-trisphosphate or sn-1,2-dipalmitoyl phosphatidylinositol 3,4-bisphosphate but is not activated by the L-enantiomers of the said phosphatidylinositol phosphates.

7. The 3-phosphoinositide-dependent protein kinase according to claim 1 which is not activated by phosphatidylinositol 3,5-bisphosphate or phosphatidylinositol 4,5-bisphosphate or phosphatidylinositol 4-phosphate or phosphatidylinositol 3-phosphate or inositol 1,3,4,5-tetrakisphosphate.

8. A method of isolating the 3-phosphoinositide-dependent protein kinase according to claim 1 , the method comprising the steps of (a) obtaining material that contains said 3-phosphoinositide-dependent protein kinase, (b) obtaining cell free extracts from said material which contain said 3-phosphoinositide-dependent protein kinase, (c) fractionating said cell free extract, and (d) selecting a fraction from step (c) which is capable of phosphorylating and activating protein kinase Bα in the presence of a 3-phosphoinositide.

9. A method of identifying a compound that modulates the activity of a 3-phosphoinositide-dependent protein kinase, the method comprising:

contacting a compound with the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity or a fusion protein comprising said fragment, and

determining whether, in the presence of said compound, phosphorylation and activation of a protein kinase B or phosphorylation of a p70 S6 kinase is changed compared to the phosphorylation and activation of a protein kinase B or phosphorylation of a p70 S6 kinase in the absence of said compound.

10. The method according to claim 9 wherein the compound decreases the activity of the 3-phosphoinositide-dependent protein kinase.

11. The method according to claim 9 wherein the compound increases the activity of the 3-phosphoinositide-dependent protein kinase.

12. The method according to claim 9 wherein the compound prevents activation of protein kinase Bα in the presence of phosphatidylinositol-3,4,5-trisphosphate or phosphatidylinositol-3,4-bisphosphate.

13. The method according to claim 9 wherein the compound modulates the activity of the 3-phosphoinositide-dependent protein kinase by binding to protein kinase Bα and preventing phosphorylation and activation of protein kinase Bα by the 3-phosphoinositide-dependent protein kinase.

14. A method of identifying a compound that mimics the effect of a 3-phosphoinositide on a 3-phosphoinositide-dependent protein kinase, the method comprising determining whether said compound activates the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity or a fusion protein comprising said fragment so that it can phosphorylate and activate a protein kinase B or phosphorylate a p70 S6 kinase, the activation by said compound being in the absence of a phosphatidylinositol-3,4,5-trisphosphate or a phosphatidylinositol-3,4-bisphosphate or another 3-phosphoinositide.

15. The method according to claim 14 wherein the 3-phosphoinositide is phosphatidylinositol-3,4,5-trisphosphate or phosphatidylinositol-3,4-bisphosphate.

16. A method of screening for compounds which modulate the activity of the 3-phosphoinositide-dependent protein kinase according to claim 1 , or a fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity or a fusion protein comprising said fragment, or compounds which modulate their interactions with a 3-phosphoinositide or with a protein kinase B, wherein said screening comprises:

contacting a compound with the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity or a fusion protein comprising said fragment and

selecting compounds which modulate the activity of said 3-phosphoinositide-dependent protein kinase according to claim 1 or a fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 or a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity or a fusion protein comprising said fragment.

17. A method of activating a protein kinase B the method comprising contacting said protein kinase B with the 3-phosphoinositide-dependent protein kinase according to claim 1 .

18. A kit comprising the substantially pure human 3-phosphoinositide-dependent protein kinase according to claim 1 , a fusion protein comprising said 3-phosphoinositide-dependent protein kinase, a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity, or a fusion protein comprising said fragment.

19. A fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 1 , a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity, or a fusion protein comprising said fragment.

20. The substantially pure 3-phosphoinositide-dependent protein kinase according to claim 1 wherein the protein kinase comprises amino acids 52-556 of SEQ ID NO:1 or amino acids 52-556 of SEQ ID NO:1 with from 1 to 4 conservative substitutions therein.

21. The fusion protein comprising the 3-phosphoinositide-dependent protein kinase according to claim 20 , a fragment of said fusion protein having 3-phosphoinositide-dependent protein kinase activity, or a fusion protein comprising said fragment.