The PIF-binding pocket in PDK1 is essential for activation of S6K and SGK, but not PKB.
PKB/Akt, S6K1 and SGK are related protein kinases activated in a PI 3-kinase-dependent manner in response to insulin/growth factors signalling. Activation entails phosphorylation of these kinases at two residues, the T-loop and the hydrophobic motif. PDK1 activates S6K, SGK and PKB isoforms by phosphorylating these kinases at their T-loop. We demonstrate that a pocket in the kinase domain of PDK1, termed the 'PIF-binding pocket', plays a key role in mediating the interaction and phosphorylation of S6K1 and SGK1 at their T-loop motif by PDK1. Our data indicate that prior phosphorylation of S6K1 and SGK1 at their hydrophobic motif promotes their interaction with the PIF-binding pocket of PDK1 and their T-loop phosphorylation. Thus, the hydrophobic motif phosphorylation of S6K and SGK converts them into substrates that can be activated by PDK1. In contrast, the PIF-binding pocket of PDK1 is not required for the phosphorylation of PKBalpha by PDK1. The PIF-binding pocket represents a substrate recognition site on a protein kinase that is only required for the phosphorylation of a subset of its physiological substrates.
Biondi
R M
RM
Division of Signal Transduction Therapy, MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB complex, University of Dundee, Dow Street, Dundee DD1 5EH, UK. r.m.biondi@dundee.ac.uk
Kieloch
A
A
Currie
R A
RA
Deak
M
M
Alessi
D R
DR
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000409:Alanine / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D004789:Enzyme Activation; D005973:Glutamine / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017874:Immediate-Early Proteins; D007532:Isoleucine / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D008239:Lysine / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D000099184:Serum-Glucocorticoid Regulated Kinases
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000409:Alanine; D005973:Glutamine; D017874:Immediate-Early Proteins; D007532:Isoleucine; D008239:Lysine; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases