TAL (transcription activator-like) effectors, secreted by phytopathogenic bacteria, recognize host DNA sequences through a central domain of tandem repeats. Each repeat comprises 33 to 35 conserved amino acids and targets a specific base pair by using two hypervariable residues [known as repeat variable diresidues (RVDs)] at positions 12 and 13. Here, we report the crystal structures of an 11.5-repeat TAL effector in both DNA-free and DNA-bound states. Each TAL repeat comprises two helices connected by a short RVD-containing loop. The 11.5 repeats form a right-handed, superhelical structure that tracks along the sense strand of DNA duplex, with RVDs contacting the major groove. The 12th residue stabilizes the RVD loop, whereas the 13th residue makes a base-specific contact. Understanding DNA recognition by TAL effectors may facilitate rational design of DNA-binding proteins with biotechnological applications.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We thank J. He and Q. Wang at Shanghai Synchrotron Radiation Facility (SSRF) beamline BL17U and K. Hasegawa and T. Kumasaka at the Spring-8 beamline BL41XU for on-site assistance. This work was supported by funds from the Ministry of Science and Technology (grant numbers 2009CB918801, 2009CB918802, and 2011CB910501); projects 30888001, 91017011, and 31070644 of the National Natural Science Foundation of China; and Tsinghua University 985 Phase II funds. Coordinates and structure factors for the DNA-free and DNA-bound structures have been deposited with the Protein Data Bank under accession codes 3V6P and 3V6T.
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