Local Sequence Targeting in the AID/APOBEC Family Differentially Impacts Retroviral Restriction and Antibody Diversification
Local Sequence Targeting in the AID/APOBEC Family Differentially Impacts Retroviral Restriction and Antibody Diversification
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DOI：
10.1074/jbc.m110.177402
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发表时间：
2010-12-24
影响因子：
4.8
通讯作者：
Stivers, James T.
中科院分区：
文献类型：
--
作者：
Kohli, Rahul M.;Maul, Robert W.;Stivers, James T.
活化诱导脱氨酶（AID）/APOBEC家族的核酸胞苷脱氨酶是主动和先天免疫应答中的关键参与者，作为靶向的、有目的的突变体发挥作用。AID特异性地使宿主免疫球蛋白（IG）位点脱氨基以进化抗体特异性，而其近亲APOBEC 3G（A3 G）使逆转录病毒病原体（如HIV）的基因组发生致命突变。了解这些酶的靶向特异性作用的基础是至关重要的，因为错误启动会带来重大风险，可能促进肿瘤发生（AID）或促进耐药性（A3 G）。AID倾向于在WRC（W = A/T，R = A/G）基序中脱胞嘧啶，而A3 G倾向于在CCC基序中脱胞嘧啶。这种特异性在很大程度上取决于识别DNA序列的酶家族中的单个发散蛋白质环。通过移植这种底物识别环，我们已经创建了具有改变的局部靶向的A3 G和AID的酶变体，以直接评估序列特异性对免疫功能的作用。我们发现，移植环放置在A3 G支架都产生了有效的限制艾滋病毒，但在AID支架的外来环妥协超突变和类转换重组。因此，局部靶向对于A3 G对逆转录病毒的先天防御似乎是可变的，但对于AID催化的适应性抗体成熟是重要的。值得注意的是，在IG基因座内的AID靶向与其体外靶向WRC序列而不是非WRC序列的能力成比例相关。虽然其他机制也可能有贡献，但我们的研究结果表明，AID/APOBEC 3酶的局部序列靶向是酶特异性与其靶DNA序列共同进化的一个很好的例子。
Nucleic acid cytidine deaminases of the activation-induced deaminase (AID)/APOBEC family are critical players in active and innate immune responses, playing roles as target-directed, purposeful mutators. AID specifically deaminates the host immunoglobulin (Ig) locus to evolve antibody specificity, whereas its close relative, APOBEC3G (A3G), lethally mutates the genomes of retroviral pathogens such as HIV. Understanding the basis for the target-specific action of these enzymes is essential, as mistargeting poses significant risks, potentially promoting oncogenesis (AID) or fostering drug resistance (A3G). AID prefers to deaminate cytosine in WRC (W = A/T, R = A/G) motifs, whereas A3G favors deamination of CCC motifs. This specificity is largely dictated by a single, divergent protein loop in the enzyme family that recognizes the DNA sequence. Through grafting of this substrate-recognition loop, we have created enzyme variants of A3G and AID with altered local targeting to directly evaluate the role of sequence specificity on immune function. We find that grafted loops placed in the A3G scaffold all produced efficient restriction of HIV but that foreign loops in the AID scaffold compromised hypermutation and class switch recombination. Local targeting, therefore, appears alterable for innate defense against retroviruses by A3G but important for adaptive antibody maturation catalyzed by AID. Notably, AID targeting within the Ig locus is proportionally correlated to its in vitro ability to target WRC sequences rather than non-WRC sequences. Although other mechanisms may also contribute, our results suggest that local sequence targeting by AID/APOBEC3 enzymes represents an elegant example of co-evolution of enzyme specificity with its target DNA sequence.