T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, United States; Program in Molecular Biophysics, Johns Hopkins University, Baltimore, United States
Jaba Mitra
Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, United States
T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, United States; Program in Molecular Biophysics, Johns Hopkins University, Baltimore, United States; Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana Champaign, Urbana, United States; Institute for Genomic Biology, University of Illinois at Urbana Champaign, Urbana, United States; Department of Biomedical Engineering, Johns Hopkins University, Baltimore, United States; Department of Biophysics and Biophysical Chemistry, Johns Hopkins University, Baltimore, United States; Howard Hughes Medical Institute, Baltimore, United States
T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, United States; Program in Molecular Biophysics, Johns Hopkins University, Baltimore, United States
Transcription activator-like effectors (TALEs) bind DNA through an array of tandem 34-residue repeats. How TALE repeat domains wrap around DNA, often extending more than 1.5 helical turns, without using external energy is not well understood. Here, we examine the kinetics of DNA binding of TALE arrays with varying numbers of identical repeats. Single molecule fluorescence analysis and deterministic modeling reveal conformational heterogeneity in both the free- and DNA-bound TALE arrays. Our findings, combined with previously identified partly folded states, indicate a TALE instability that is functionally important for DNA binding. For TALEs forming less than one superhelical turn around DNA, partly folded states inhibit DNA binding. In contrast, for TALEs forming more than one turn, partly folded states facilitate DNA binding, demonstrating a mode of ‘functional instability’ that facilitates macromolecular assembly. Increasing repeat number slows down interconversion between the various DNA-free and DNA-bound states.
