Wanner Roger M, Castor Dennis, Güthlein Carolin, Böttger Erik C, Springer Burkhard, Jiricny Josef
Institute of Medical Microbiology, University of Zurich, and National Centre for Mycobacteria, Gloriastrasse 30, CH-8006 Zurich,Switzerland.
J Bacteriol. 2009 Oct;191(20):6312-9. doi: 10.1128/JB.00613-09. Epub 2009 Aug 14.
Spontaneous hydrolytic deamination of DNA bases represents a considerable mutagenic threat to all organisms, particularly those living in extreme habitats. Cytosine is readily deaminated to uracil, which base pairs with adenine during replication, and most organisms encode at least one uracil DNA glycosylase (UDG) that removes this aberrant base from DNA with high efficiency. Adenine deaminates to hypoxanthine approximately 10-fold less efficiently, and its removal from DNA in vivo has to date been reported to be mediated solely by alkyladenine DNA glycosylase. We previously showed that UdgB from Pyrobaculum aerophilum, a hyperthermophilic crenarchaeon, can excise hypoxanthine from oligonucleotide substrates, but as this organism is not amenable to genetic manipulation, we were unable to ascertain that the enzyme also has this role in vivo. In the present study, we show that UdgB from Mycobacterium smegmatis protects this organism against mutagenesis associated with deamination of both cytosine and adenine. Together with Ung-type uracil glycosylase, M. smegmatis UdgB also helps attenuate the cytotoxicity of the antimicrobial agent 5-fluorouracil.
DNA碱基的自发水解脱氨基作用对所有生物体，尤其是生活在极端环境中的生物体，构成了相当大的诱变威胁。胞嘧啶很容易脱氨基变成尿嘧啶，尿嘧啶在复制过程中与腺嘌呤形成碱基对，大多数生物体至少编码一种尿嘧啶DNA糖基化酶（UDG），这种酶能高效地从DNA中去除这种异常碱基。腺嘌呤脱氨基变成次黄嘌呤的效率大约低10倍，迄今为止，据报道腺嘌呤在体内从DNA中的去除仅由烷基腺嘌呤DNA糖基化酶介导。我们之前表明，嗜热栖热袍菌（一种嗜热泉古菌）中的UdgB可以从寡核苷酸底物中切除次黄嘌呤，但由于这种生物体不适合进行基因操作，我们无法确定该酶在体内是否也具有此功能。在本研究中，我们表明耻垢分枝杆菌中的UdgB可保护该生物体免受与胞嘧啶和腺嘌呤脱氨基相关的诱变作用。与Ung型尿嘧啶糖基化酶一起，耻垢分枝杆菌UdgB还有助于减轻抗菌剂5-氟尿嘧啶的细胞毒性。
