Please use this identifier to cite or link to this item: https://doi.org/10.1186/1471-2091-6-19
Title: Biochemical characterization of Cdk2-Speedy/Ringo A2
Authors: Cheng, A
Gerry, S
Kaldis, P 
Solomon, M.J
Keywords: cyclin dependent kinase 2
histone
peptide
article
biochemistry
cell culture
cell cycle
cell cycle S phase
cell maturation
comparative study
enzyme activation
enzyme activity
human
human cell
metazoon
oocyte
protein function
protein phosphorylation
Xenopus
Amino Acid Substitution
Animals
Cattle
Cyclin-Dependent Kinase 2
Humans
Phosphorylation
Metazoa
Issue Date: 2005
Citation: Cheng, A, Gerry, S, Kaldis, P, Solomon, M.J (2005). Biochemical characterization of Cdk2-Speedy/Ringo A2. BMC Biochemistry 6 : 19. ScholarBank@NUS Repository. https://doi.org/10.1186/1471-2091-6-19
Rights: Attribution 4.0 International
Abstract: Background: Normal cell cycle progression requires the precise activation and inactivation of cyclin-dependent protein kinases (CDKs), which consist of a CDK and a cyclin subunit. A novel cell cycle regulator called Speedy/Ringo shows no sequence similarity to cyclins, yet can directly bind to and activate CDKs. Speedy/Ringo proteins, which bind to and activate Cdc2 and Cdk2 in vitro, are required for the G2 to M transition during Xenopus oocyte maturation and for normal S-phase entry in cultured human cells. Results: We have characterized the substrate specificity and enzymatic activity of human Cdk2-Speedy/Ringo A2 in order to gain insights into the possible functions of this complex. In contrast to Cdk2-cyclin A, which has a well-defined consensus target site ((S/T)PX(K/R)) that strongly favors substrates containing a lysine at the +3 position of substrates, Cdk2-Speedy/Ringo A2 displayed a broad substrate specificity at this position. Consequently, Cdk2-Ringo/Speedy A2 phosphorylated optimal Cdk2 substrates such as histone H1 and a KSPRK peptide poorly, only ?0.08% as well as Cdk2-cyclin A, but non-canonical Cdk2 substrates such as a KSPRY peptide relatively well, with an efficiency of ?80% compared to Cdk2-cyclin A. Cdk2-Speedy/Ringo A2 also phosphorylated authentic Cdk2 substrates, such as Cdc25 proteins, which contain non-canonical CDK phosphorylation sites, nearly as well as Cdk2-cyclin A. Phosphopeptide mapping indicated that Cdk2-Speedy/Ringo A2 and Cdk2-cyclin A phosphorylate distinct subsets of sites on Cdc25 proteins. Thus, the low activity that Cdk2-Speedy/Ringo A2 displays when assayed on conventional Cdk2 substrates may significantly underestimate the potential physiological importance of Cdk2-Speedy/Ringo A2 in phosphorylating key subsets of Cdk2 substrates. Unlike Cdk2-cyclin A, whose activity depends strongly on activating phosphorylation of Cdk2 on Thr-160, neither the overall catalytic activity nor the substrate recognition by Cdk2-Speedy/Ringo A2 was significantly affected by this phosphorylation. Furthermore, Cdk2-Speedy/Ringo A2 was not a suitable substrate for metazoan CAK (which phosphorylates Cdk2 at Thr-160), supporting the notion that Speedy/Ringo A2 activates Cdk2 in a CAK-independent manner. Conclusion: There are major differences in substrate preferences between CDK-Speedy/Ringo A2 and Cdk2-cyclin complexes. These differences may accommodate the CAK-independent activation of Cdk2 by Speedy/Ringo A2 and they raise the possibility that CDK-Speedy/Ringo A2 complexes could phosphorylate and regulate a subset of non-canonical CDK substrates, such as Cdc25 protein phosphatases, to control cell cycle progression. © 2005 Cheng et al; licensee BioMed Central Ltd.
Source Title: BMC Biochemistry
URI: https://scholarbank.nus.edu.sg/handle/10635/178028
ISSN: 14712091
DOI: 10.1186/1471-2091-6-19
Rights: Attribution 4.0 International
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