Maillard Olivier, Solyom Szilvia, Naegeli Hanspeter
Institute of Pharmacology and Toxicology, University of Zurich-Vetsuisse, Zurich, Switzerland.
PLoS Biol. 2007 Apr;5(4):e79. doi: 10.1371/journal.pbio.0050079.
It was not known how xeroderma pigmentosum group C (XPC) protein, the primary initiator of global nucleotide excision repair, achieves its outstanding substrate versatility. Here, we analyzed the molecular pathology of a unique Trp690Ser substitution, which is the only reported missense mutation in xeroderma patients mapping to the evolutionary conserved region of XPC protein. The function of this critical residue and neighboring conserved aromatics was tested by site-directed mutagenesis followed by screening for excision activity and DNA binding. This comparison demonstrated that Trp690 and Phe733 drive the preferential recruitment of XPC protein to repair substrates by mediating an exquisite affinity for single-stranded sites. Such a dual deployment of aromatic side chains is the distinctive feature of functional oligonucleotide/oligosaccharide-binding folds and, indeed, sequence homologies with replication protein A and breast cancer susceptibility 2 protein indicate that XPC displays a monomeric variant of this recurrent interaction motif. An aversion to associate with damaged oligonucleotides implies that XPC protein avoids direct contacts with base adducts. These results reveal for the first time, to our knowledge, an entirely inverted mechanism of substrate recognition that relies on the detection of single-stranded configurations in the undamaged complementary sequence of the double helix.
作为全球核苷酸切除修复的主要启动因子，着色性干皮病C组（XPC）蛋白是如何实现其卓越的底物通用性尚不清楚。在此，我们分析了一种独特的Trp690Ser替代的分子病理学，这是唯一报道的着色性干皮病患者错义突变，定位于XPC蛋白的进化保守区域。通过定点诱变，随后筛选切除活性和DNA结合，测试了这个关键残基和相邻保守芳香族氨基酸的功能。这种比较表明，Trp690和Phe733通过介导对单链位点的精细亲和力，驱动XPC蛋白优先募集到修复底物上。芳香侧链的这种双重作用是功能性寡核苷酸/寡糖结合折叠的独特特征，实际上，与复制蛋白A和乳腺癌易感蛋白2的序列同源性表明，XPC展示了这种反复出现的相互作用基序的单体变体。对与受损寡核苷酸结合厌恶表明，XPC蛋白避免与碱基加合物直接接触。据我们所知，这些结果首次揭示了一种完全相反的底物识别机制，该机制依赖于在双螺旋未受损互补序列中检测单链构型。
