Carpenter Elisabeth P, Corbett Anne, Thomson Hellen, Adacha Jolanta, Jensen Kirsten, Bergeron Julien, Kasampalidis Ioannis, Exley Rachel, Winterbotham Megan, Tang Christoph, Baldwin Geoff S, Freemont Paul
Centre for Structural Biology, Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, London, UK.
EMBO J. 2007 Mar 7;26(5):1363-72. doi: 10.1038/sj.emboj.7601593. Epub 2007 Feb 22.
Oxidative stress is a principal cause of DNA damage, and mechanisms to repair this damage are among the most highly conserved of biological processes. Oxidative stress is also used by phagocytes to attack bacterial pathogens in defence of the host. We have identified and characterised two apurinic/apyrimidinic (AP) endonuclease paralogues in the human pathogen Neisseria meningitidis. The presence of multiple versions of DNA repair enzymes in a single organism is usually thought to reflect redundancy in activities that are essential for cellular viability. We demonstrate here that these two AP endonuclease paralogues have distinct activities in DNA repair: one is a typical Neisserial AP endonuclease (NApe), whereas the other is a specialised 3'-phosphodiesterase Neisserial exonuclease (NExo). The lack of AP endonuclease activity of NExo is shown to be attributable to the presence of a histidine side chain, blocking the abasic ribose-binding site. Both enzymes are necessary for survival of N. meningitidis under oxidative stress and during bloodstream infection. The novel functional pairing of NExo and NApe is widespread among bacteria and appears to have evolved independently on several occasions.
氧化应激是DNA损伤的主要原因，而修复这种损伤的机制是生物过程中最保守的机制之一。吞噬细胞也利用氧化应激来攻击细菌病原体以保护宿主。我们已经在人类病原体脑膜炎奈瑟菌中鉴定并表征了两种脱嘌呤/脱嘧啶（AP）内切核酸酶旁系同源物。通常认为在单个生物体中存在多个版本的DNA修复酶反映了对细胞活力至关重要的活性的冗余。我们在此证明这两种AP内切核酸酶旁系同源物在DNA修复中具有不同的活性：一种是典型的奈瑟菌AP内切核酸酶（NApe），而另一种是专门的3'-磷酸二酯酶奈瑟菌核酸外切酶（NExo）。结果表明，NExo缺乏AP内切核酸酶活性是由于存在组氨酸侧链，从而阻断了无碱基核糖结合位点。这两种酶对于脑膜炎奈瑟菌在氧化应激下和血流感染期间的存活都是必需的。NExo和NApe的这种新型功能配对在细菌中广泛存在，并且似乎已经在多个场合独立进化。
