Hsu Gerald W, Huang Xuanwei, Luneva Natalia P, Geacintov Nicholas E, Beese Lorena S
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Biol Chem. 2005 Feb 4;280(5):3764-70. doi: 10.1074/jbc.M411276200. Epub 2004 Nov 16.
Of the carcinogens to which humans are most frequently exposed, the polycyclic aromatic hydrocarbon benzo[a]pyrene (BP) is one of the most ubiquitous. BP is a byproduct of grilled foods and tobacco and fuel combustion and has long been linked to various human cancers, particularly lung and skin. BP is metabolized to diol epoxides that covalently modify DNA bases to form bulky adducts that block DNA synthesis by replicative or high fidelity DNA polymerases. Here we present the structure of a high fidelity polymerase from a thermostable strain of Bacillus stearothermophilus (Bacillus fragment) bound to the most common BP-derived N2-guanine adduct base-paired with cytosine. The BP adduct adopts a conformation that places the polycyclic BP moiety in the nascent DNA minor groove and is the first structure of a minor groove adduct bound to a polymerase. Orientation of the BP moiety into the nascent DNA minor groove results in extensive disruption to the interactions between the adducted DNA duplex and the polymerase. The disruptions revealed by the structure of Bacillus fragment bound to a BP adduct provide a molecular basis for rationalizing the potent blocking effect on replication exerted by BP adducts.
在人类最常接触的致癌物中，多环芳烃苯并[a]芘（BP）是最普遍存在的致癌物之一。BP是烤制食品、烟草和燃料燃烧的副产物，长期以来一直与各种人类癌症相关，尤其是肺癌和皮肤癌。BP被代谢为二醇环氧化物，这些二醇环氧化物会与DNA碱基发生共价修饰，形成大的加合物，从而通过复制性或高保真DNA聚合酶阻断DNA合成。在这里，我们展示了来自嗜热脂肪芽孢杆菌（芽孢杆菌片段）的一种高保真聚合酶与最常见的BP衍生的与胞嘧啶碱基配对的N2-鸟嘌呤加合物结合的结构。BP加合物采取一种构象，将多环BP部分置于新生DNA的小沟中，这是与聚合酶结合的小沟加合物的首个结构。BP部分进入新生DNA小沟的方向导致加合的DNA双链体与聚合酶之间的相互作用受到广泛破坏。与BP加合物结合的芽孢杆菌片段的结构所揭示的这些破坏为合理化BP加合物对复制产生的强大阻断作用提供了分子基础。
