Fan Li, Arvai Andrew S, Cooper Priscilla K, Iwai Shigenori, Hanaoka Fumio, Tainer John A
Life Sciences Division, Department of Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Mol Cell. 2006 Apr 7;22(1):27-37. doi: 10.1016/j.molcel.2006.02.017.
The human xeroderma pigmentosum group B (XPB) helicase is essential for transcription, nucleotide excision repair, and TFIIH functional assembly. Here, we determined crystal structures of an Archaeoglobus fulgidus XPB homolog (AfXPB) that characterize two RecA-like XPB helicase domains and discover a DNA damage recognition domain (DRD), a unique RED motif, a flexible thumb motif (ThM), and implied conformational changes within a conserved functional core. RED motif mutations dramatically reduce helicase activity, and the DRD and ThM, which flank the RED motif, appear structurally as well as functionally analogous to the MutS mismatch recognition and DNA polymerase thumb domains. Substrate specificity is altered by DNA damage, such that AfXPB unwinds dsDNA with 3' extensions, but not blunt-ended dsDNA, unless it contains a lesion, as shown for CPD or (6-4) photoproducts. Together, these results provide an unexpected mechanism of DNA unwinding with implications for XPB damage verification in nucleotide excision repair.
人类着色性干皮病B组（XPB）解旋酶对于转录、核苷酸切除修复及TFIIH功能组装至关重要。在此，我们确定了嗜热栖热菌XPB同源物（AfXPB）的晶体结构，该结构表征了两个类RecA的XPB解旋酶结构域，并发现了一个DNA损伤识别结构域（DRD）、一个独特的RED基序、一个灵活的拇指基序（ThM），以及保守功能核心内隐含的构象变化。RED基序突变显著降低解旋酶活性，且位于RED基序两侧的DRD和ThM在结构和功能上似乎类似于MutS错配识别结构域和DNA聚合酶拇指结构域。DNA损伤会改变底物特异性，使得AfXPB能够解开具有3'端延伸的双链DNA，但不能解开平端双链DNA，除非其含有损伤，如CPD或（6-4）光产物所示。这些结果共同提供了一种意想不到的DNA解旋机制，对核苷酸切除修复中XPB损伤验证具有重要意义。
