From the Division of Biochemistry, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
J Biol Chem. 2013 Nov 1;288(44):31624-34. doi: 10.1074/jbc.M113.491928. Epub 2013 Sep 24.
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.
Geminin 是后生动物增殖和分化的重要调控因子，主要抑制 DNA 复制许可因子 Cdt1，防止基因组过度复制。我们表明 Geminin 优先与同源物 Idas 形成稳定的卷曲螺旋异二聚体。与 Idas-Geminin 异二聚体相比，Idas 同源二聚体热力学不稳定，在生理条件下不太可能作为稳定的大分子存在。Idas 与 Geminin 同源区复合物的晶体结构显示出紧密的头对头异二聚体卷曲螺旋。这种 Idas-Geminin 异二聚体与 Geminin-Geminin 相比，与 Cdt1 的结合力较弱，但亲和力仍很高（∼30nm），但热力学性质明显不同。一致地，在非洲爪蟾卵提取物中，与 Geminin-Geminin 同源二聚体相比，Idas-Geminin 在抑制许可方面的活性较低。在人培养细胞中，Idas 的异位表达导致有限的过度复制，而 Geminin 的共表达则抵消了这种过度复制。Idas-Geminin 复合物的特性表明它是 Idas 的功能形式，并提供了一种调节 Geminin 活性的可能机制。
