Characterizing Tyrosine Ring Flips in Proteins by 19F NMR

Aromatic ring-flip dynamics are hallmarks of concerted protein "breathing" motions that are essential for biological function. Ring flips occur on a broad range of timescales (ns-s) and have been primarily studied by NMR spectroscopy, typically requiring expensive isotope labeling of aromatic side chains, thereby limiting such studies to a few proteins. Here, we report two novel di-fluorotyrosine probes, 3,5-F2Y and 2,6-F2Y, that can be incorporated into proteins cost-effectively for characterizing and modulating tyrosine ring-flip dynamics. We show that 19F rotating-frame (R1{rho}) relaxation dispersion is powerful for quantifying ring flips on the {micro}s-ms timescale. Importantly, the tyrosine ring-flip rates (kflip) for 3,5-F2Y in GB1 and HPr are comparable to those measured by 1H and 13C NMR studies, validating 3,5-F2Y as a largely non-perturbing, native-like ring-flip probe. In contrast, 2,6-F2Y acts as an effective "brake" on ring flips, enabling direct visualization and quantitative characterization of previously undetected tyrosine ring flips in ubiquitin via 19F lineshape analysis. Furthermore, we use 2,6-F2Y to assess the environmental effects on ring-flip dynamics in crowding reagents and in living X. laevis oocytes. Collectively, our study opens a new avenue for measuring and modulating ring-flip dynamics in vitro and in living cells. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC="FIGDIR/small/630691v2_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@dcf8e1org.highwire.dtl.DTLVardef@1578887org.highwire.dtl.DTLVardef@1c481d0org.highwire.dtl.DTLVardef@268ae0_HPS_FORMAT_FIGEXP M_FIG C_FIG