User:Fatma Abukhater/Cyclin-dependent kinase
Cyclin-dependent kinases (CDKs) are a predominant group of serine/threonine protein kinases involved in the regulation of the cell cycle and its progression, ensuring the integrity and functionality of cellular machinery. These regulatory enzymes play a crucial role in the regulation of eukaryotic cell cycle and transcription, as well as DNA repair, metabolism, and epigenetic regulation, in response to several extracellular and intracellular signals.[1] [2] They are present in all known eukaryotes, and their regulatory function in the cell cycle has been evolutionarily conserved.[3] [4] The catalytic activities of CDKs are regulated by interactions with CDK inhibitors (CKIs) and regulatory subunits known as cyclins. Cyclins have no enzymatic activity themselves, but they become active once they bind to CDKs. Without cyclin, CDK is less active than in the cyclin-CDK heterodimer complex.[5][6] CDKs phosphorylate proteins on serine (S) or threonine (T) residues. The specificity of CDKs for their substrates is defined by the S/T-P-X-K/R sequence, where S/T is the phosphorylation site, P is proline, X is any amino acid, and the sequence ends with lysine (K) or arginine (R). This motif ensures CDKs accurately target and modify proteins, crucial for regulating cell cycle and other functions.[7] Deregulation of the CDK activity is linked to various pathologies, including cancer, neurodegenerative diseases, and stroke. [6]
Evolutionary History
[edit]CDKs were initially identified through studies in model organisms such as yeasts and frogs, underscoring their pivotal role in cell cycle progression. These enzymes operate by forming complexes with cyclins, whose levels fluctuate throughout the cell cycle, thereby ensuring timely cell cycle transitions. Over the years, the understanding of CDKs has expanded beyond cell division to include roles in gene transcription integration of cellular signals. [7] [8]
The evolutionary journey of CDKs has led to a diverse family with specific members dedicated to cell cycle phases or transcriptional control. For instance, budding yeast expresses six distinct CDKs, with some binding multiple cyclins for cell cycle control and others binding with a single cyclin for transcription regulation. In humans, the expansion to 20 CDKs and 29 cyclins illustrates their complex regulatory roles. Key CDKs such as CDK1 are indispensable for cell cycle control, while others like CDK2 and CDK3 are not. Moreover, transcriptional CDKs, such as CDK7 in humans, play crucial roles in initiating transcription by phosphorylating RNA polymerase II (RNAPII), indicating the intricate link between cell cycle regulation and transcriptional management. This evolutionary expansion from simple regulators to multifunctional enzymes underscores the critical importance of CDKs in the complex regulatory networks of eukaryotic cells.[7]
Species | Name | Original name | Size (amino acids) | Function |
---|---|---|---|---|
Saccharomyces cerevisiae | CDK1 | Cdc28 | 298 | All cell-cycle stages |
Schizosaccharomyces pombe | CDK1 | Cdc2 | 297 | All cell-cycle stages |
Drosophila melanogaster | CDK1 | Cdc2 | 297 | M |
CDK2 | Cdc2c | 314 | G1/S, S, possibly M | |
CDK4 | Cdk4/6 | 317 | G1, promotes growth | |
Xenopus laevis | Cdk1 | Cdc2 | 301 | M |
CDK2 | 297 | S, possibly M | ||
Homo sapiens | Cdk1 | Cdc2 | 297 | M |
CDK2 | 298 | G1, S, possibly M | ||
CDK4 | 301 | G1 | ||
CDK6 | 326 | G1 |
CDKs and Cyclins in the Cell Cycle
[edit]CDK is one of the estimated 800 human protein kinases. CDKs have low molecular weight, and they are known to be inactive by themselves. They are characterized by their dependency on the regulatory subunit, cyclin. The activation of CDKs also requires post-translational modifications involving phosphorylation reactions. This phosphorylation typically occurs on a specific threonine residue, leading to a conformational change in the CDK that enhances its kinase activity. [9] The activation forms a cyclin-CDK complex which phosphorylates specific regulatory proteins that are required to initiate steps in the cell-cycle.[5]
![](http://up.wiki.x.io/wikipedia/commons/thumb/c/c9/CDKs_in_cell_cycle.png/220px-CDKs_in_cell_cycle.png)
In human cells, the CDK family comprises 20 different members that play a crucial role in the regulation of the cell cycle and transcription. These are usually separated into cell-cycle CDKs, which regulate cell-cycle transitions and cell division, and transcriptional CDKs, which mediate gene transcription. CDK1, CDK2, CDK3, CDK4, CDK6, and CDK7are directly related to the regulation of cell-cycle events, while CDK7 – 11 are associated with transcriptional regulation.[1] Different cyclin-CDK complexes regulate different phases of the cell cycle, known as G0/G1, S, G2, and M phases, featuring several checkpoints to maintain genomic stability and ensure accurate DNA replication.[1][5] Cyclin-CDK complexes of earlier cell-cycle phase help activate cyclin-CDK complexes in later phase.[4]
CDK | Cyclin partner | Established functions |
---|---|---|
CDK1 | cyclin B | M phase transition |
CDK2 | cyclin A | G1/S transition |
CDK2 | cyclin E | S/G2 transition |
CDK3 | cyclin C | G0/G1 and G1/S transitions |
CDK4, CDK6 | cyclin D | G1/S transition. Phosphorylation of retinoblastoma gene product (Rb) |
CDK7 | cyclin H | CAK and RNAPII transcription |
CDK Structure and Activation
[edit]Cyclin-dependent kinases (CDKs) mainly consist of a two-lobed configuration, which is characteristic of all kinases in general. CDKs have specific features in their structure that play a major role in their function and regulation.[2]
- N-terminal lobe (N-lobe): In this part, the inhibitory element known as the glycine-rich G-loop is located. The inhibitory element is found within the beta-sheets in this N-terminal lobe.[4][2] Additionally, there is a helix known as the C-helix. This helix contains the PSTAIRE sequence in CDK1. This region plays a crucial role in regulating the binding between cyclin-dependent kinases (CDKs) and cyclins.[7][2]
- C-terminal lobe (C-lobe): This part contains α-helices and the activation segment, which extends from the DFG motif (D145 in CDK2) to the APE motif (E172 in CDK2). This segment also includes a phosphorylation-sensitive residue (T160 in CDK2) in the so-called T-loop. The activation segment in the C-lobe serves as a platform for the binding of the phospho-acceptor Ser/Thr region of substrates.[7][4][2]
Cyclin Binding
[edit]The active site, or ATP-binding site, in all kinases is a cleft located between a smaller amino-terminal lobe and a larger carboxy-terminal lobe. Research on the structure of human CDK2 has shown that CDKs have a specially adapted ATP-binding site that can be regulated through the binding of cyclin. Phosphorylation by CDK-activating kinase (CAK) at Thr160 in the T-loop helps to increase the complex's activity. Without cyclin, a flexible loop known as the activation loop or T-loop blocks the cleft, and the positioning of several key amino acids is not optimal for ATP binding.[2][10] With cyclin, two alpha helices change position to enable ATP binding. One of them, the L12 helix located just before the T-loop in the primary sequence, is transformed into a beta strand and helps to reorganize the T-loop so that it no longer blocks the active site. The other alpha helix, known as the PSTAIRE helix, is reorganized and helps to change the position of the key amino acids in the active site.[6][10]
There's considerable specificity in which cyclin binds to CDK. Furthermore, the cyclin binding determines the specificity of the cyclin-CDK complex for certain substrates, highlighting the importance of distinct activation pathways that confer cyclin-binding specificity on CDK1. This illustrates the complexity and fine-tuning in the regulation of the cell cycle through selective binding and activation of CDKs by their respective cyclins.[11][12]
Cyclins can directly bind the substrate or localize the CDK to a subcellular area where the substrate is found. The RXL-binding site was crucial in revealing how CDKs selectively enhance activity toward specific substrates by facilitating substrate docking.[13] Substrate specificity of S cyclins is imparted by the hydrophobic batch, which has affinity for substrate proteins that contain a hydrophobic RXL (or Cy) motif.[4] Cyclin B1 and B2 can localize Cdk1 to the nucleus and the Golgi, respectively, through a localization sequence outside the CDK-binding region.[4]
References
[edit]- ^ a b c d Ding, Lei; Jiaqi, Cao; Wen, Lin; Hongijan, Chen; Xianhui, Xiong; Hongshun, Ao; Min, Yu; Jie, Lin; Qinghua, Cui (2020). "The Roles of Cyclin-Dependent Kinases in Cell-Cycle Progression and Therapeutic Strategies in Human Breast Cancer". International journal of molecular sciences. 21 (6). doi:10.3390/ijms21061960.
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: CS1 maint: unflagged free DOI (link) - ^ a b c d e f Hives, Mark; Jurecekova, Jana; Holeckova, Klaudia Hives; Kliment, Jan; Sivonova, Monika Kmetova (2023). "The driving power of the cell cycle: cyclin-dependent kinases, cyclins and their inhibitors". Bratislavske Lekarske Listy. 124 (4): 261–266. doi:10.4149/BLL_2023_039. ISSN 0006-9248. PMID 36598318.
- ^ S, Gokul Babu; Gohil, Deependra Singh; Roy Choudhury, Swarup (2023-01-19). "Genome-wide identification, evolutionary and expression analysis of the cyclin-dependent kinase gene family in peanut". BMC Plant Biology. 23 (1): 43. doi:10.1186/s12870-023-04045-w. ISSN 1471-2229. PMC 9850575. PMID 36658501.
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: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ a b c d e f g O Morgan, David (2007). The Cell Cycle: Principles of Control. London: New Science Press Ltd. pp. 2–54, 196–266. ISBN 978-0-9539181-2-6.
- ^ a b c d Alberts, Bruce; Hopkin, Karen; Johnson, Alexander; Morgan, David; Raff, Martin; Roberts, Keith; Walter, Peter (2019). Essential Cell Biology (5th ed.). W. W. Norton & Company. pp. 613–627. ISBN 9780393679533.
- ^ a b c d Łukasik, Paweł; Załuski, Michał; Gutowska, Izabela (2021-03-13). "Cyclin-Dependent Kinases (CDK) and Their Role in Diseases Development–Review". International Journal of Molecular Sciences. 22 (6): 2935. doi:10.3390/ijms22062935. ISSN 1422-0067. PMC 7998717. PMID 33805800.
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: CS1 maint: unflagged free DOI (link) - ^ a b c d e Malumbres, Marcos (2014-06-30). "Cyclin-dependent kinases". Genome Biology. 15 (6): 122. doi:10.1186/gb4184. ISSN 1474-760X.
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: CS1 maint: unflagged free DOI (link) - ^ Barberis, Matteo (2021-12-13). "Cyclin/Forkhead-mediated coordination of cyclin waves: an autonomous oscillator rationalizing the quantitative model of Cdk control for budding yeast". npj Systems Biology and Applications. 7 (1): 1–11. doi:10.1038/s41540-021-00201-w. ISSN 2056-7189.
- ^ Knockaert, Marie; Meijer, Laurent (2002-09-01). "Identifying in vivo targets of cyclin-dependent kinase inhibitors by affinity chromatography". Biochemical Pharmacology. Cell Signaling, Transcription and Translation as Therapeutic Targets. 64 (5): 819–825. doi:10.1016/S0006-2952(02)01144-9. ISSN 0006-2952.
- ^ a b Li, Yan; Zhang, Jingxiao; Gao, Weimin; Zhang, Lilei; Pan, Yanqiu; Zhang, Shuwei; Wang, Yonghua (2015-04-24). "Insights on Structural Characteristics and Ligand Binding Mechanisms of CDK2". International Journal of Molecular Sciences. 16 (5): 9314–9340. doi:10.3390/ijms16059314. ISSN 1422-0067. PMC 4463590. PMID 25918937.
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: CS1 maint: unflagged free DOI (link) - ^ Merrick, Karl A.; Larochelle, Stéphane; Zhang, Chao; Allen, Jasmina J.; Shokat, Kevan M.; Fisher, Robert P. (2008-12-05). "Distinct activation pathways confer cyclin-binding specificity on Cdk1 and Cdk2 in human cells". Molecular Cell. 32 (5): 662–672. doi:10.1016/j.molcel.2008.10.022. ISSN 1097-4164. PMC 2643088. PMID 19061641.
- ^ Massacci, Giorgia; Perfetto, Livia; Sacco, Francesca (2023). "The Cyclin-dependent kinase 1: more than a cell cycle regulator". British Journal of Cancer. 129 (11): 1707–1716. doi:10.1038/s41416-023-02468-8. ISSN 1532-1827.
- ^ Wood, Daniel J.; Endicott, Jane A. (2018). "Structural insights into the functional diversity of the CDK–cyclin family". Open Biology. 8 (9). doi:10.1098/rsob.180112. ISSN 2046-2441. PMC 6170502. PMID 30185601.
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: CS1 maint: PMC format (link)