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首页> 外文期刊>Biochemistry >Redesigning the substrate specificity of human O(6)-alkylguanine-DNA alkyltransferase. Mutants with enhanced repair of O(4)-methylthymine.
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Redesigning the substrate specificity of human O(6)-alkylguanine-DNA alkyltransferase. Mutants with enhanced repair of O(4)-methylthymine.

机译:重新设计人类O(6)-烷基鸟嘌呤-DNA烷基转移酶的底物特异性。具有增强的O(4)-甲基胸腺嘧啶修复的突变体。

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摘要

Human O(6)-alkylguanine-DNA alkyltransferase (MGMT) repairs potentially cytotoxic and mutagenic alkylation damage at the O(6)-position of guanine and the O(4)-position of thymine in DNA. We have used random sequence mutagenesis and functional complementation to obtain human MGMT mutants that are resistant to the MGMT inhibitor, O(6)-benzylguanine [Encell, L. P., Coates, M. M., and Loeb, L. A. (1998) Cancer Res. 58, 1013-1020]. Here we describe screening of O(6)-benzylguanine-resistant mutants for altered substrate specificity, i.e., for an increased level of utilization of O(4)-methylthymine (m(4)T) relative to that of O(6)-methylguanine (m(6)G). One mutant identified by the screen, 56-8, containing eight substitutions near the active site (C150Y, S152R, A154S, V155G, N157T, V164M, E166Q, and A170T), was purified and characterized kinetically. The second-order rate constant for repair of m(4)T by the mutant was up to 11.5-fold greater than that of WT MGMT, and the relative m(4)T specificity, k(m(4)T)/k(m(6)G), was as much as 75-fold greater. In competition experiments with both substrates present, the mutant was 277-fold more sensitive to inhibition by m(4)T than WT MGMT. This mutant, and others like it, could help elucidate the complex relationship between adduction at specific sites in DNA and the cytotoxicity and mutagenicity of alkylating agents.
机译:人的O(6)-烷基鸟嘌呤-DNA烷基转移酶(MGMT)修复DNA中鸟嘌呤的O(6)-位和胸腺嘧啶的O(4)-位潜在的细胞毒性和诱变烷基化损伤。我们已经使用随机序列诱变和功能互补来获得对MGMT抑制剂O(6)-苄基鸟嘌呤具有抗性的人MGMT突变体[Encell,L.P.,Coates,M.M.和Loeb,L.A.(1998)Cancer Res。 58,1013-1020]。在这里,我们描述了针对改变的底物特异性,即相对于O(6)-的O(4)-甲基胸腺嘧啶(m(4)T)利用水平的提高,对O(6)-苄基鸟嘌呤抗性突变体的筛选甲基鸟嘌呤(m(6)G)。筛选并鉴定了通过筛选鉴定的一个突变体56-8,该突变体在活性位点附近有八个取代(C150Y,S152R,A154S,V155G,N157T,V164M,E166Q和A170T)。突变体修复m(4)T的二级速率常数比WT MGMT高21.5倍,相对m(4)T特异性为k(m(4)T)/ k (m(6)G),高出75倍。在存在两种底物的竞争实验中,该突变体对m(4)T的抑制作用比WT MGMT高277倍。这种突变体,以及其他类似的突变体,可以帮助阐明DNA中特定位点的内含与烷基化剂的细胞毒性和致突变性之间的复杂关系。

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