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. Author manuscript; available in PMC: 2016 Nov 4.
Published in final edited form as: Chembiochem. 2016 Jul 13;17(17):1636–1642. doi: 10.1002/cbic.201600265

Figure 4.

Figure 4

Impact of the oxygen-to-sulfur substitutions on the intermolecular ion pair with Lys57. (A) Overlaid Lys side-chain NH3+-selective 1H-15N HISQC spectra[17] recorded for the four complexes of the Antp homeodomain and DNA. These complexes chemically differ only in the DNA phosphate at the Lys57 interaction site (black, unmodified; blue, RP-monothioated; red, SP-monothioated; and magenta, dithioated). (B) Change in NMR-derived order parameters S2axis for Lys NH3+ groups upon oxygen-to-sulfur substitution in DNA phosphate at the Lys57 interaction site. The data for the unmodified and dithioated DNA complexes are from our previous study.[5d] These data show that sulfur substitution of the proximal phosphate oxygen (i.e., OP2) atom significantly mobilizes the Lys side-chain NH3+ group.