The Eukaryotic Linear Motif resource for
Functional Sites in Proteins
Functional site class:
AGC Kinase docking motif
Functional site description:
The AGC kinases constitute a large family of serine/threonine protein kinases consisting of 60 members, including the cAMP- and cGMP-dependent protein kinases (PKA and PKG), the protein kinase C family (PKC), PKB/Akt, ribosomal protein S6 kinases, and the 3-phosphoinositide-dependent protein kinase (PDK1). They regulate many critical processes including metabolism and cell proliferation. Members of this family contain a hydrophobic surface in the N-terminal lobe of their catalytic domain, called the PDK1 Interacting Fragment (PIF) pocket, and a non-catalytic C-terminal tail containing different motifs, including the AGCK docking motif that interacts with the PIF pocket. Both these regions are conserved in Eukaryotic AGC kinases, except for PDK1, which lacks the C-tail. The AGCK docking motif mediates intramolecular interactions to the PIF pocket, serving as a cis-activating module, but can also act as a PDK1 docking site that trans-activates PDK1, which in turn will phosphorylate the docked AGC kinase.
ELMs with same func. site: DOC_AGCK_PIF_1  DOC_AGCK_PIF_2  DOC_AGCK_PIF_3 
ELM Description:
The AGCK docking motif of some AGC kinases, including p70 and p90 ribosomal kinases (S6K and RSK, respectively) and serum/glucocorticoid-regulated kinases (SGK), contains a phosphorylatable serine/threonine residue flanked by an aromatic residue on either side. The residue directly upstream is most frequently but not exclusively a phenylalanine, while the residue downstream is either a phenylalanine or a tyrosine. An additional aromatic residue four residues upstream of the phospho-acceptor site is invariantly a phenylalanine. Although the PDK1 PIF pocket shows a higher affinity for the phosphorylated motif, the precise role of motif phosphorylation in regulating cis-activation of the kinase and docking to PDK1 is still unclear. While some evidence indicates that phosphorylation of the AGCK docking motif of S6K controls its activation by PDK1 (Frodin,2002, Collins,2005), others suggest that phosphorylation of the motif is not required for activation of S6K by PDK1, but instead occurs after PDK1 has phosphorylated the activation loop of S6K and, once phosphorylated, the motif will fully activate S6K by operating in cis (Keshwani,2011). Similarly, for the conventional PKC beta isoform, it has been shown that, although its AGCK docking motif has a higher affinity for PDK1 when it is phosphorylated, PDK1 preferentially associates with the unphosphorylated enzyme. Release of PDK1 is followed by autophosphorylation of the motif and subsequent cis-activation of PKC by the phosphorylated motif (Gao,2001). Also concerning the role of the PKB hydrophobic motif in docking to and trans-activation of PDK1, conflicting results have been obtained, possibly due to a difference in experimental conditions (Biondi,2001, Scheid,2002). The mechanisms and kinases involved in phosphorylation of the AGCK docking motif differ for the different kinases.
Pattern: F..[FWY][ST][FY]
Pattern Probability: 0.0000038
Present in taxon: Eukaryota
Interaction Domain:
Pkinase (PF00069) Protein kinase domain (Stochiometry: 1 : 1)
o See 10 Instances for DOC_AGCK_PIF_1
o Abstract
This entry covers an auto-activating linear motif of AGC group kinases. Several variants of the motif exist, and for many kinases, the motif has been shown to operate in trans to bind and activate the upstream activating kinase PDK1. To make matters more complicated, some variants are regulated by phosphorylation.
The AGC kinases regulate critical processes including metabolism, cell growth, proliferation, survival and differentiation, hence deregulation of these enzymes is a causative factor in different diseases such as cancer and diabetes. Solved structures of AGC kinases show the typical bilobal kinase fold of the kinase domain, consisting of a small N-terminal lobe (N-lobe) and a larger C-terminal lobe (C-lobe). Regulation of kinase activity is mainly achieved through phosphorylation of the activation or T-loop, located in the C-lobe and connected to the N-lobe through the alpha-C helix. This modification results in conformational changes, mainly in the alpha-C helix, that reposition key catalytic and substrate binding residues. Sandwiched between the N- and C-lobe is an ATP-binding site that provides the phosphate-donor during phosphorylation. Repositioning of the alpha-C helix upon kinase activation allows formation of a salt bridge between an alpha-C helix glutamate and a conserved lysine residue within the beta-3 strand that interacts with the alpha and beta phosphates of ATP (Pearce,2010).
The non-catalytic C-terminal tail of the kinase is also involved in repositioning of the alpha-C helix. The alpha-C helix is part of a hydrophobic pocket and an adjacent phosphate-binding site in the N-lobe, called the PIF pocket, which interacts with the AGCK docking motif (PDK1 Interacting Fragment (PIF) / hydrophobic motif (HM)) that is present in the C-tail of AGC kinases. This interaction stabilizes the active conformation of the alpha-C helix through an allosteric mechanism. Both the PIF pocket and the C-terminal region are conserved in Eukaryotic AGC kinases, except for PDK1, which lacks the C-terminal part. The AGCK docking motif mediates intramolecular interactions to the PIF pocket, serving as a cis-activating module, together with other regulatory sequences present in the C-tail of the kinase. However, in some kinases it also serves as a PDK1 docking site that trans-activates PDK1, which itself does not possess this regulatory region. Activated PDK1 in turn will phosphorylate and activate the docked AGC kinase (Mora,2004).
Several AGC kinases are involved in mediating signaling downstream of phosphatidyl-inositol-4,5-bisphosphate 3-kinase (PI3K) in response to a wide range of stimuli such as growth factors and hormones. PDK1 functions as a common upstream activator by phosphorylating the other AGC kinases at their activation loop. The PDK1 PIF pocket serves both as an allosteric regulatory site for PDK1 activity and as a docking site for the AGC kinases it phosphorylates, by binding to the AGCK docking motif that is present in the C-tail of its substrates. AGC kinases in their inactive state have an incompatible PIF pocket due to the alpha-C helix being disordered, meaning that their AGCK docking motif is available for binding to the PIF pocket of PDK1, which becomes trans-activated. After being phosphorylated by PDK1, the AGCK docking motif can engage in an intramolecular interaction with its functional PIF pocket, resulting in release from PDK1 and full activation of the kinase.
The AGCK docking motif generally appears as three aromatic residues, most often phenylalanines, surrounding a phosphorylatable serine or threonine residue (DOC_AGCK_PIF_1). Phosphorylation of this serine/threonine increases the affinity of the motif for the PIF pocket, which allows fine-tuning the cis and trans interactions of the motif. The mechanisms and kinases involved in phosphorylation of the AGCK docking motif differ for the different kinases. Some alternative patterns of the motif exist. In atypical PKC forms and PKC-like (PKN) kinases, the phosphorylatable serine or threonine residue is replaced by an acidic phosphomimetic aspartate or glutamate residue (DOC_AGCK_PIF_2). In other AGC kinases, including PKA, the motif is located at the very C-terminal and contains only the first two core aromatic residues (DOC_AGCK_PIF_3). In many cases, full activation of the AGC kinases is also dependent on additional signals that are specific for each kinase and that provide spatial and conformational regulation.
o 14 selected references:

o 7 GO-Terms:

o 10 Instances for DOC_AGCK_PIF_1
(click table headers for sorting; Notes column: =Number of Switches, =Number of Interactions)
Acc., Gene-, NameStartEndSubsequenceLogic#Ev.OrganismNotes
P11792 SCH9
733 738 SPAMQAKFAGFTFVDESAID TP 4 Saccharomyces cerevisiae S288c
P31751 AKT2
470 475 LELDQRTHFPQFSYSASIRE TP 1 Homo sapiens (Human)
Q9ERE3 Sgk3
482 487 VLEADDAFVGFSYAPPSEDL TP 3 Mus musculus (House mouse)
482 487 VLEADDAFVGFSYAPPSEDL TP 3 Homo sapiens (Human)
O00141 SGK1
418 423 VKEAAEAFLGFSYAPPTDSF TP 6 Homo sapiens (Human)
P67999 Rps6kb1
408 413 SESANQVFLGFTYVAPSVLE TP 6 Rattus norvegicus (Norway rat)
P18654 Rps6ka3
382 387 SANAHQLFRGFSFVAITSDD TP 3 Mus musculus (House mouse)
Q13464 ROCK1
394 399 FVGNQLPFVGFTYYSNRRYL TP 3 Homo sapiens (Human)
P31749 AKT1
469 474 VDSERRPHFPQFSYSASGTA U 8 Homo sapiens (Human)
P05771-2 PRKCB
656 661 RNIDQSEFEGFSFVNSEFLK TP 2 Homo sapiens (Human)
Please cite: The Eukaryotic Linear Motif resource: 2022 release. (PMID:34718738)

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