Journal of Molecular Biology
Walter J. Johnson Prize: reviewMechanisms of cyclin-dependent kinase regulation: structures of cdks, their cyclin activators, and cip and INK4 inhibitors1, 2
Section snippets
The cyclin-dependent kinases
The cell cycle coordinates events needed for the growth of all eukaryotic cells, events such as DNA replication (S phase) and cell division (M phase), ensuring that they occur in the right temporal sequence and proceed in an orderly fashion (reviewed by Sherr 1994, Nurse 1994, King et al 1994). In addition, the cell cycle receives and integrates signals from diverse growth regulatory pathways, ensuring that the cell grows only in the presence of the appropriate signals and in the right
Cdk regulation
Cdks are regulated by several different processes, perhaps reflecting the diversity of the signaling pathways that converge on them. Figure 1(a) summarizes the major regulatory processes common to most Cdks. There are a few additional regulatory processes for subsets of Cdks (reviewed by Morgan, 1995).
When first synthesized, the isolated Cdk subunit has no detectable activity. Its activation occurs in a two-step process. One step is the binding of a cyclin subunit, which imparts partial
The monomeric Cdk
The structure of monomeric Cdk2 has the same overall fold as other eukaryotic protein kinases, first seen in the structure of the cAMP-dependent protein kinase (PKA; Knighton et al., 1991). The structure consists of an N-terminal lobe rich in β-sheet (N lobe), a larger C-terminal lobe rich in α-helix (C lobe), and a deep cleft at the junction of the two lobes that is the site of ATP binding and catalysis (Figure 1(b)). In the monomeric Cdk2 structure, two regions differed from the canonical
Cyclin binding and partial activation
In this step of the activation process, the cyclin binds to one side of the catalytic cleft interacting with both lobes and forming a continuous protein-protein interface (Figure 1(b)). CyclinA contacts to the PSTAIRE helix have a key role in the interface, explaining why cyclin-dependent kinases but not cyclin-independent kinases have this characteristic sequence. Other key contacts are made to the T loop, and parts of the N and C lobes (Jeffrey et al., 1995).
Cyclin binding activates the
Phosphorylation and complete activation
When the T loop becomes phosphorylated on Thr160 (Cdk2), it undergoes an additional conformational change (Figure 3; Russo et al., 1996b). This change is induced by the phosphate group acting as an organizing center in this region, being bound by three arginine side-chains, each coming from a different part of the structure (one from the N lobe, one from the C lobe, and one from the T loop). The arginine residues, in turn, hydrogen bond to other Cdk and cyclin groups, and extend the organizing
Inhibition of the Cdk-cyclin complex by the Cip family
The fully active form of the enzyme can be completely shut down by the binding of the Cip family of inhibitors. One member of the family, p27Cip2, is shown in Figure 1(b) binding the phosphorylated Cdk2-cyclinA complex, interacting with both the Cdk and the cyclin (Russo et al., 1996a).
The obvious mechanism through which p27 inhibits the kinase is through the insertion of a small, 310-helix inside the catalytic cleft (Figure 1(b)). A comparison of the p27-Cdk2-cyclinA and the ATP-Cdk2-cyclinA
Cdk-inhibition by the INK4 family
In the structure of the p16INK4a bound to Cdk6 Russo et al 1998, Brotherton et al 1998, the inhibitor binds next to the catalytic cleft, opposite from where the cyclin would bind, and interacts with both the N and C lobes to form a continuous interface (Figure 1(b)). The INK4 and cyclin binding sites on the Cdk do not overlap, and this explains how INK4 proteins can bind to the Cdk-cyclin complex without dissociating the cyclin.
But if the INK4 and cyclin binding sites do not overlap, how does
Cdks posses an intrinsic conformational flexibility
It is remarkable that all these processes that regulate Cdks at the molecular level work through conformational changes, often so large that they may be better described as structural changes. These recurring structural changes indicate that the Cdk possesses an intrinsic structural flexibility, especially in and around the catalytic cleft (Russo et al., 1998).
Revisiting the mechanisms of Cdk regulation with this intrinsic structural flexibility in mind, it appears that the monomeric Cdk has
Acknowledgements
The author thanks Alicia A. Russo, Philip D. Jeffrey, Lily Tong and Andrea Patten, whose structural studies of the Cdk complexes made this review possible; David O. Morgan for his help with these studies; and Christine Murray for help with the manuscript. The author’s laboratory is supported by the NIH, the Howard Hughes Medical Institute, the Dewitt Wallace Foundation, and the Samuel and Rudin May Foundation.
References (33)
- et al.
WAF1, a potential mediator of p53 tumor suppression
Cell
(1993) - et al.
A novel cyclin associates with MO15/CDK7 to form the CDK-activating kinase
Cell
(1994) - et al.
Cyclins and cancer. IIcyclin D and CDK inhibitors come of age
Cell
(1994) - et al.
The Cdk-activating kinase (CAK) from budding yeast
Cell
(1996) - et al.
Mitosis in transition
Cell
(1994) p53, the cellular gatekeeper for growth and division
Cell
(1997)Ordering S phase and M phase in the cell cycle
Cell
(1994)- et al.
Cloning of p27Kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals
Cell
(1994) The tumor suppressor protein p16INK4a
Exp. Cell Res.
(1997)G1 phase progressioncycling on cue
Cell
(1994)
A requirement for caveolin-1 and associated kinase Fyn in integrin signaling and anchorage-dependent cell growth
Cell
Involvement of the cyclin-dependent kinase inhibitor p16 (INK4a) in replicative senescence of normal human fibroblasts
Proc. Natl Acad. Sci. USA
Crystal structure of the complex of the cyclin D-dependent kinase Cdk6 bound to the cell-cycle inhibitor p19INK4d
Nature
Crystal structure of cyclin-dependent kinase 2
Nature
A cyclin-dependent kinase-activating kinase (CAK) in budding yeast unrelated to vertebrate CAK
Science
Mechanism of CDK activation revealed by the structure of a cyclinA-CDK2 complex
Nature
Cited by (588)
Novel thioxoimidazolidinone derivatives as dual EGFR and CDK2 inhibitors: Design, synthesis, anticancer evaluation with in silico study
2023, Journal of Molecular StructureSynthesis and biological evaluation of novel pteridin-7(8H)-one derivatives as potent CDK2 inhibitors
2023, Bioorganic and Medicinal Chemistry LettersCyclin-dependent kinase 2 (CDK2)
2023, Metalloenzymes: From Bench to BedsideGingerol/letrozole-loaded mesoporous silica nanoparticles for breast cancer therapy: In-silico and in-vitro studies
2022, Microporous and Mesoporous Materials
- 1
1998 Awardee, Walter J. Johnson Prize for the Encouragement of Research in the Life Sciences
- 2
Edited by P. E. Wright