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Tükenmez H, Magnussen HM, Kovermann M, Byström A, Wolf-Watz M. Linkage between Fitness of Yeast Cells and Adenylate Kinase Catalysis. PLoS One 2016; 11:e0163115. [PMID: 27642758 PMCID: PMC5028032 DOI: 10.1371/journal.pone.0163115] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 09/03/2016] [Indexed: 01/08/2023] Open
Abstract
Enzymes have evolved with highly specific values of their catalytic parameters kcat and KM. This poses fundamental biological questions about the selection pressures responsible for evolutionary tuning of these parameters. Here we are address these questions for the enzyme adenylate kinase (Adk) in eukaryotic yeast cells. A plasmid shuffling system was developed to allow quantification of relative fitness (calculated from growth rates) of yeast in response to perturbations of Adk activity introduced through mutations. Biophysical characterization verified that all variants studied were properly folded and that the mutations did not cause any substantial differences to thermal stability. We found that cytosolic Adk is essential for yeast viability in our strain background and that viability could not be restored with a catalytically dead, although properly folded Adk variant. There exist a massive overcapacity of Adk catalytic activity and only 12% of the wild type kcat is required for optimal growth at the stress condition 20°C. In summary, the approach developed here has provided new insights into the evolutionary tuning of kcat for Adk in a eukaryotic organism. The developed methodology may also become useful for uncovering new aspects of active site dynamics and also in enzyme design since a large library of enzyme variants can be screened rapidly by identifying viable colonies.
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Affiliation(s)
- Hasan Tükenmez
- Department of Molecular Biology, Umeå University, SE-901 87, Umeå, Sweden
| | | | | | - Anders Byström
- Department of Molecular Biology, Umeå University, SE-901 87, Umeå, Sweden
- * E-mail: (MWW); (AB)
| | - Magnus Wolf-Watz
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
- * E-mail: (MWW); (AB)
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Blank HM, Sheltzer JM, Meehl CM, Amon A. Mitotic entry in the presence of DNA damage is a widespread property of aneuploidy in yeast. Mol Biol Cell 2015; 26:1440-51. [PMID: 25694455 PMCID: PMC4395125 DOI: 10.1091/mbc.e14-10-1442] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Accepted: 02/11/2015] [Indexed: 11/11/2022] Open
Abstract
Aneuploidy causes DNA replication defects and premature adaptation to DNA damage, with profound consequences for genome stability. Such abnormalities provide the substrate for translocations and deletions that are a hallmark of cancer. Genetic instability is a hallmark of aneuploidy in budding and fission yeast. All aneuploid yeast strains analyzed to date harbor elevated levels of Rad52-GFP foci, a sign of DNA damage. Here we investigate how continuously elevated levels of DNA damage affect aneuploid cells. We show that Rad52-GFP foci form during S phase, consistent with the observation that DNA replication initiation and elongation are impaired in some aneuploid yeast strains. We furthermore find that although DNA damage is low in aneuploid cells, it nevertheless has dramatic consequences. Many aneuploid yeast strains adapt to DNA damage and undergo mitosis despite the presence of unrepaired DNA leading to cell death. Wild-type cells exposed to low levels of DNA damage exhibit a similar phenotype, indicating that adaptation to low levels of unrepaired DNA is a general property of the cell's response to DNA damage. Our results indicate that by causing low levels of DNA damage, whole-chromosome aneuploidies lead to DNA breaks that persist into mitosis. Such breaks provide the substrate for translocations and deletions that are a hallmark of cancer.
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Affiliation(s)
- Heidi M Blank
- Koch Institute for Integrative Cancer Research, Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Jason M Sheltzer
- Koch Institute for Integrative Cancer Research, Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Colleen M Meehl
- Koch Institute for Integrative Cancer Research, Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Angelika Amon
- Koch Institute for Integrative Cancer Research, Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139
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Adenylate Kinase Isoform Network: A Major Hub in Cell Energetics and Metabolic Signaling. SYSTEMS BIOLOGY OF METABOLIC AND SIGNALING NETWORKS 2014. [DOI: 10.1007/978-3-642-38505-6_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Huo L, Wu R, Yu Z, Zhai Y, Yang X, Chan TC, Yeung JTF, Kan J, Liang C. The Rix1 (Ipi1p-2p-3p) complex is a critical determinant of DNA replication licensing independent of their roles in ribosome biogenesis. Cell Cycle 2012; 11:1325-39. [PMID: 22421151 DOI: 10.4161/cc.19709] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Several replication-initiation proteins are assembled stepwise onto replicators to form pre-replicative complexes (pre-RCs) to license eukaryotic DNA replication. We performed a yeast functional proteomic screen and identified the Rix1 complex members (Ipi1p-Ipi2p/Rix1-Ipi3p) as pre-RC components and critical determinants of replication licensing and replication-initiation frequency. Ipi3p interacts with pre-RC proteins, binds chromatin predominantly at ARS sequences in a cell cycle-regulated and ORC- and Noc3p-dependent manner and is required for loading Cdc6p, Cdt1p and MCM onto chromatin to form pre-RC during the M-to-G₁ transition and for pre-RC maintenance in G₁ phase-independent of its role in ribosome biogenesis. Moreover, Ipi1p and Ipi2p, but not other ribosome biogenesis proteins Rea1p and Utp1p, are also required for pre-RC formation and maintenance, and Ipi1p, -2p and -3p are interdependent for their chromatin association and function in pre-RC formation. These results establish a new framework for the hierarchy of pre-RC proteins, where the Ipi1p-2p-3p complex provides a critical link between ORC-Noc3p and Cdc6p-Cdt1p-MCM in replication licensing.
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Affiliation(s)
- Lin Huo
- Division of Life Science, Center for Cancer Research and State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Kowloon, Hong Kong, China
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Wu R, Wang J, Liang C. Cdt1p, through its interaction with Mcm6p, is required for the formation, nuclear accumulation and chromatin loading of the MCM complex. J Cell Sci 2012; 125:209-19. [PMID: 22250202 DOI: 10.1242/jcs.094169] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Regulation of DNA replication initiation is essential for the faithful inheritance of genetic information. Replication initiation is a multi-step process involving many factors including ORC, Cdt1p, Mcm2-7p and other proteins that bind to replication origins to form a pre-replicative complex (pre-RC). As a prerequisite for pre-RC assembly, Cdt1p and the Mcm2-7p heterohexameric complex accumulate in the nucleus in G1 phase in an interdependent manner in budding yeast. However, the nature of this interdependence is not clear, nor is it known whether Cdt1p is required for the assembly of the MCM complex. In this study, we provide the first evidence that Cdt1p, through its interaction with Mcm6p with the C-terminal regions of the two proteins, is crucial for the formation of the MCM complex in both the cytoplasm and nucleoplasm. We demonstrate that disruption of the interaction between Cdt1p and Mcm6p prevents the formation of the MCM complex, excludes Mcm2-7p from the nucleus, and inhibits pre-RC assembly and DNA replication. Our findings suggest a function for Cdt1p in promoting the assembly of the MCM complex and maintaining its integrity by interacting with Mcm6p.
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Affiliation(s)
- Rentian Wu
- Division of Life Science and Center for Cancer Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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Musgrove EA, Sutherland RL. RB in breast cancer: differential effects in estrogen receptor-positive and estrogen receptor-negative disease. Cell Cycle 2011; 9:4607. [PMID: 21260944 DOI: 10.4161/cc.9.23.13889] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Zhai Y, Yung PYK, Huo L, Liang C. Cdc14p resets the competency of replication licensing by dephosphorylating multiple initiation proteins during mitotic exit in budding yeast. J Cell Sci 2010; 123:3933-43. [DOI: 10.1242/jcs.075366] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In eukaryotes, replication licensing is achieved through sequential loading of several replication-initiation proteins onto replication origins to form pre-replicative complexes (pre-RCs), and unscheduled replication licensing is prevented by cyclin-dependent kinases (CDKs) through inhibitory phosphorylations of multiple initiation proteins. It is known that CDK inactivation during mitotic exit promotes pre-RC formation for the next cell cycle. However, whether the removal of the inhibitory phosphorylations on the initiation proteins is essential and the identity of the acting phosphatase(s) remain unknown. Here, we show that cell division cycle protein 14 (Cdc14p) dephosphorylates replication-initiation proteins Orc2p, Orc6p, Cdc6p and Mcm3p to restore their competence for pre-RC assembly in the budding yeast Saccharomyces cerevisiae. Cells without functional Cdc14p fail to dephosphorylate initiation proteins and to form pre-RCs – even when CDK activities are suppressed – and cannot replicate DNA in mitotic rereplication systems, whereas pulsed ectopic expression of Cdc14p in mitotic cells results in efficient pre-RC assembly and DNA rereplication. Furthermore, Cdc14p becomes dispensable for DNA rereplication in mitotic cells with combined non-phosphorylatable and/or phosphorylation-insensitive alleles of the initiation proteins. These data unravel the essential role of Cdc14p in replication licensing, beyond its established functions in mitotic exit, providing new insight into the intricate regulation of DNA replication through the interplay of CDKs and the Cdc14p phosphatase.
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Affiliation(s)
- Yuanliang Zhai
- Section of Biochemistry and Cell Biology, Division of Life Science, and Center for Cancer Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Philip Y. K. Yung
- Section of Biochemistry and Cell Biology, Division of Life Science, and Center for Cancer Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Lin Huo
- Section of Biochemistry and Cell Biology, Division of Life Science, and Center for Cancer Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Chun Liang
- Section of Biochemistry and Cell Biology, Division of Life Science, and Center for Cancer Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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