Binding of MutS mismatch repair protein to DNA containing UV photoproducts, "mismatched" opposite Watson-Crick and novel nucleotides, in different DNA sequence contexts
Binding of MutS mismatch repair protein to DNA containing UV photoproducts, "mismatched" opposite Watson-Crick and novel nucleotides, in different DNA sequence contexts
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DOI：
10.1016/j.dnarep.2005.04.018
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发表时间：
2005-08-15
期刊：
影响因子：
3.8
通讯作者：
Hays, JB
中科院分区：
文献类型：
--
作者：
Hoffman, PD;Wang, HX;Hays, JB
错配修复(MMR)系统通过纠正DNA复制错误(碱基-错对)和对突变DNA损伤的反应来抑制突变。MutS同源蛋白-细菌MutS、真核MSH2中心点MSH6(MutSα)和MSH2中心点MSH3-选择性结合错配或损坏的DNA，启动错配纠正途径和对病变的反应，并可能累积增加下游步骤的分辨。因此，MUTS同源结合的选择性和众所周知但鲜为人知的DNA序列上下文对识别的影响可能是MMR特异性和效率的主要决定因素。调节紫外线诱变的MMR过程可能始于MutS同系物选择性结合“不匹配”的T[CPD]T/AG和T[6-4]T/AG光产物，这是先前报道的hMutSa和这里描述的E.Coli MutS蛋白。如果MMR通过直接作用于复制旁路的预致突变产物来抑制紫外线诱变，则在大多数DNA序列环境中应该识别不匹配的光产物。在这里测试的四个上下文中的三个(三个本质上不同)，T[CPD]T/AG与MutS的结合仅略好于T[CPD]T/AA或同源双链DNA；两个测试的上下文中只有一个促进了T[6-4]T/AG的选择性结合。虽然T[CPD]T/AG和T/G中的T：G对都采用摆动构象，但MutS在所有情况下都很好地结合了T/G(K-1/2 2.1-2.9 nm)。因此，MutS似乎通过不同的机制选择了这两个错配。其他地方的核磁共振分析表明，在(高度扭曲的)T[6-4]T/AG中，3‘胸腺嘧啶的02个与环1-亚氨基和外环2-氨基鸟嘌呤质子之间的分叉氢键稳定了一种新的平面结构，这在T[6-4]T/AA中是不可能的。如预测的那样，用缺少一个质子(肌苷、2-氨基嘌呤)或两个质子(烟碱)的嘌呤取代G可显著减少或消除选择性的MutS结合。以前的研究和这里的工作加在一起，表明在大约一半的DNA序列背景下，MutS(可能还有MutSα)可以选择性地结合不匹配的紫外光产物，并直接抑制紫外线诱变。(C)2005 Elsevier B.V.保留所有权利。
Mismatch-repair (MMR) systems suppress mutation via correction of DNA replication errors (base-mispairs) and responses to mutagenic DNA lesions. Selective binding of mismatched or damaged DNA by MutS-homolog proteins-bacterial MutS, eukaryotic MSH2 center dot MSH6 (MutS alpha) and MSH2 center dot MSH3-initiates mismatch-correction pathways and responses to lesions, and may cumulatively increase discrimination at downstream steps. MutS-homolog binding selectivity and the well-known but poorly understood effects of DNA-sequence contexts on recognition may thus be primary determinants of MMR specificity and efficiency. MMR processes that modulate UV mutagenesis might begin with selective binding by MutS homologs of "mismatched" T[CPD]T/AG and T[6-4]T/AG photoproducts, reported previously for hMutSa and described here for E. coli MutS protein. If MMR suppresses UV mutagenesis by acting directly on pre-mutagenic products of replicative bypass, mismatched photoproducts should be recognized in most DNA-sequence contexts. In three of four contexts tested here (three substantially different), T[CPD]T/AG was bound only slightly better by MutS than was T[CPD]T/AA or homoduplex DNA; only one of two contexts tested promoted selective binding of T[6-4]T/AG. Although the T:G pairs in T[CPD]T/AG and T/G both adopt wobble conformations, MutS bound T/G well in all contexts (K-1/2 2.1-2.9 nM). Thus, MutS appears to select the two mismatches by different mechanisms. NMR analyses elsewhere suggest that in the (highly distorted) T[6-4]T/AG a forked H-bond between 02 of the 3' thymine and the ring 1-imino and exocyclic 2-amino guanine protons stabilizes a novel planar structure not possible in T[6-4]T/AA. Replacement of G by purines lacking one (inosine, 2-aminopurine) or both (nebularine) protons markedly reduced or eliminated selective MutS binding, as predicted. Previous studies and the work here, taken together, suggest that in only about half of DNA sequence contexts could MutS (and presumably Muts alpha) selectively bind mismatched UV photoproducts and directly suppress UV mutagenesis. (c) 2005 Elsevier B.V. All rights reserved.