The Geminin and Idas Coiled Coils Preferentially Form a Heterodimer That Inhibits Geminin Function in DNA Replication Licensing |
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Authors: | Christophe Caillat Dafni-Eleftheria Pefani Peter J Gillespie Stavros Taraviras J Julian Blow Zoi Lygerou Anastassis Perrakis |
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Institution: | From the ‡Division of Biochemistry, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.;§Laboratory of Biology, School of Medicine, University of Patras, 26505 Rio, Patras, Greece.;¶Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom, and ;‖Laboratory of Physiology, School of Medicine, University of Patras, 26505 Rio, Patras, Greece |
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Abstract: | Geminin is an important regulator of proliferation and differentiation in metazoans, which predominantly inhibits the DNA replication licensing factor Cdt1, preventing genome over-replication. We show that Geminin preferentially forms stable coiled-coil heterodimers with its homologue, Idas. In contrast to Idas-Geminin heterodimers, Idas homodimers are thermodynamically unstable and are unlikely to exist as a stable macromolecule under physiological conditions. The crystal structure of the homology regions of Idas in complex with Geminin showed a tight head-to-head heterodimeric coiled-coil. This Idas-Geminin heterodimer binds Cdt1 less strongly than Geminin-Geminin, still with high affinity (∼30 nm), but with notably different thermodynamic properties. Consistently, in Xenopus egg extracts, Idas-Geminin is less active in licensing inhibition compared with a Geminin-Geminin homodimer. In human cultured cells, ectopic expression of Idas leads to limited over-replication, which is counteracted by Geminin co-expression. The properties of the Idas-Geminin complex suggest it as the functional form of Idas and provide a possible mechanism to modulate Geminin activity. |
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Keywords: | DNA Replication Isothermal Titration Calorimetry Protein Stability X-ray Crystallography X-ray Scattering Xenopus Coiled Coil |
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