The Bipolar Filaments Formed by Herpes Simplex Virus Type 1 SSB/Recombination Protein (ICP8) Suggest a Mechanism for DNA Annealing
The Bipolar Filaments Formed by Herpes Simplex Virus Type 1 SSB/Recombination Protein (ICP8) Suggest a Mechanism for DNA Annealing
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DOI：
10.1016/j.jmb.2008.12.059
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发表时间：
2009-02-20
影响因子：
5.6
通讯作者：
Egelman, Edward H.
中科院分区：
文献类型：
--
作者：
Makhov, Alexander M.;Sen, Anindito;Egelman, Edward H.
I型单纯疱疹病毒编码多功能蛋白ICP 8，其既作为单链结合蛋白又作为重组酶，催化涉及病毒基因组复制和重组的反应。在二价离子存在下和低温下，之前的电子显微镜研究表明ICP 8会形成长的左手螺旋丝。在这里，电子显微镜图像重建显示，丝是双极的，与一个不对称的单位包含两个亚基的ICP 8，构成一个对称的二聚体。使用扫描透射电子显微镜已经证实了这种组织的细丝。丝的节距类似于250埃，每圈类似于6.2个二聚体。ICP 8的晶体结构与重构细丝的对接显示，通过含有类似于10个残基的柔性接头连接到亚基主体的ICP 8的C-末端结构域以与细丝中类似的方式被填充到晶体中相邻亚基主体中的口袋中。然而，大的N-末端域之间的相互作用是完全不同的长丝中所观察到的晶体。先前提出的ICP 8结合单链DNA（ssDNA）的模型，基于晶体结构，导致一个模型的连续链的ssDNA的丝轴附近。ICP 8细丝的双极性质意味着ssDNA的第二条链将以相反的方向穿过该细丝，这为ICP 8如何将互补ssDNA退火成双链DNA提供了潜在的机制，其中每条链以相反的方向延伸。(C)2009爱思唯尔有限公司版权所有。
Herpes simplexvirus type I encodes a multifunctional protein, ICP8, which serves both as a single-strand binding protein and as a recombinase, catalyzing reactions involved in replication and recombination of the viral genome. In the presence of divalent ions and at low temperature, previous electron microscopic studies showed that ICP8 will form long left-handed helical filaments. Here, electron microscopic image reconstruction reveals that the filaments are bipolar, with an asymmetric unit containing two subunits of ICP8 that constitute a symmetrical dimer. This organization of the filament has been confirmed using scanning transmission electron microscopy. The pitch of the filaments is similar to 250 angstrom, with similar to 6.2 dimers per turn. Docking of a crystal structure of ICP8 into the reconstructed filament shows that the C-terminal domain of ICP8, attached to the body of the subunit by a flexible linker containing similar to 10 residues, is packed into a pocket in the body of a neighboring subunit in the crystal in a similar manner as in the filament. However, the interactions between the large N-terminal domains are quite different in the filament from that observed in the crystal. A previously proposed model for ICP8 binding single-stranded DNA (ssDNA), based upon the crystal structure, leads to a model for a continuous strand of ssDNA near the filament axis. The bipolar nature of the ICP8 filaments means that a second strand of ssDNA would be running through this filament in the opposite orientation, and this provides a potential mechanism for how ICP8 anneals complementary ssDNA into double-stranded DNA, where each strand runs in opposite directions. (C) 2009 Elsevier Ltd. All rights reserved.