State Key Laboratory of Bio-membrane and Membrane Biotechnology, Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua-Peking Center for Life Sciences, Beijing, 100084, China.
Protein Cell. 2014 Apr;5(4):297-306. doi: 10.1007/s13238-014-0035-2. Epub 2014 Mar 14.
Transcription activator-like (TAL) effectors specifically bind to double stranded (ds) DNA through a central domain of tandem repeats. Each TAL effector (TALE) repeat comprises 33-35 amino acids and recognizes one specific DNA base through a highly variable residue at a fixed position in the repeat. Structural studies have revealed the molecular basis of DNA recognition by TALE repeats. Examination of the overall structure reveals that the basic building block of TALE protein, namely a helical hairpin, is one-helix shifted from the previously defined TALE motif. Here we wish to suggest a structure-based re-demarcation of the TALE repeat which starts with the residues that bind to the DNA backbone phosphate and concludes with the base-recognition hyper-variable residue. This new numbering system is consistent with the α-solenoid superfamily to which TALE belongs, and reflects the structural integrity of TAL effectors. In addition, it confers integral number of TALE repeats that matches the number of bound DNA bases. We then present fifteen crystal structures of engineered dHax3 variants in complex with target DNA molecules, which elucidate the structural basis for the recognition of bases adenine (A) and guanine (G) by reported or uncharacterized TALE codes. Finally, we analyzed the sequence-structure correlation of the amino acid residues within a TALE repeat. The structural analyses reported here may advance the mechanistic understanding of TALE proteins and facilitate the design of TALEN with improved affinity and specificity.
转录激活因子样效应物（TAL）通过串联重复的中央结构域特异性结合双链 DNA。每个 TAL 效应物（TALE）重复包含 33-35 个氨基酸，通过重复中固定位置的高度可变残基识别一个特定的 DNA 碱基。结构研究揭示了 TALE 重复识别 DNA 的分子基础。对整体结构的检查表明，TALE 蛋白的基本构建块，即螺旋发夹，相对于先前定义的 TALE 基序，在一个螺旋上发生了一个螺旋的位移。在这里，我们希望基于结构重新划分 TALE 重复，从与 DNA 骨架磷酸盐结合的残基开始，到碱基识别超变残基结束。这个新的编号系统与 TALE 所属的α-螺旋超家族一致，反映了 TAL 效应物的结构完整性。此外，它赋予了与结合的 DNA 碱基数量相匹配的完整的 TALE 重复数。然后，我们展示了十五个工程化的 dHax3 变体与目标 DNA 分子复合物的晶体结构，这些结构阐明了报道或未表征的 TALE 密码子识别腺嘌呤（A）和鸟嘌呤（G）碱基的结构基础。最后，我们分析了 TALE 重复内氨基酸残基的序列-结构相关性。这里报告的结构分析可能会推进对 TALE 蛋白的机制理解，并促进设计具有改进亲和力和特异性的 TALEN。
