Pezza Roberto J, Petukhova Galina V, Ghirlando Rodolfo, Camerini-Otero R Daniel
Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA.
J Biol Chem. 2006 Jul 7;281(27):18426-34. doi: 10.1074/jbc.M601073200. Epub 2006 May 4.
The mouse Hop2 and Mnd1 proteins, which can form a stable heterodimeric complex, ensure the proper synapsis of homologous chromosomes in meiosis by acting in concert with Rad51 and Dmc1 to promote the strand invasion (D-loop formation) step of homologous recombination. Hop2 alone promotes D-loop formation, but Mnd1 and the Hop2-Mnd1 complex do not. Here we show that only the heterodimer complex, but not the individual proteins, can stimulate strand invasion by Dmc1. Furthermore, we demonstrate that the interaction with Mnd1 provokes changes in Hop2 that are responsible not only for abrogating the recombinase activity of Hop2 but also for generating a new molecular interface able to physically interact with and stimulate Dmc1. We also show that coiled-coil motifs in Hop2 and Mnd1 are essential for their interaction with each other and that a clearly delineated region near the COOH terminus of both proteins is necessary for both the DNA binding and single-strand annealing by the Hop-Mnd1 heterodimer. Finally, we describe a point mutation in Hop2 that dissociates its strand invasion activity from its ability to bind and anneal DNA.
小鼠的Hop2和Mnd1蛋白能够形成稳定的异源二聚体复合物，它们与Rad51和Dmc1协同作用，促进同源重组的链入侵（D环形成）步骤，从而确保减数分裂中同源染色体的正确联会。单独的Hop2可促进D环形成，但Mnd1以及Hop2-Mnd1复合物则不能。我们在此表明，只有异源二聚体复合物，而非单个蛋白，能够刺激Dmc1介导的链入侵。此外，我们证明与Mnd1的相互作用会引发Hop2的变化，这些变化不仅消除了Hop2的重组酶活性，还产生了一个能够与Dmc1进行物理相互作用并刺激其活性的新分子界面。我们还表明，Hop2和Mnd1中的卷曲螺旋基序对于它们彼此间的相互作用至关重要，并且这两种蛋白COOH末端附近一个明确界定的区域对于Hop-Mnd1异源二聚体的DNA结合和单链退火都是必需的。最后，我们描述了Hop2中的一个点突变，该突变使其链入侵活性与其结合和退火DNA的能力相分离。
