Cross-polarization magic-angle spinning and rotational-echo double resonance 13C and 15N NMR experiments have been performed on intact cells of Staphylococcus aureus labeled with D-[1-13C]alanine and [15N]glycine or with [1-13C]glycine and L-[epsilon-15N]lysine. The cells were harvested during stationary or exponential growth conditions, the latter in media with and without the addition of vancomycin. The results of these experiments allowed the in situ determination of the relative concentrations of peptidoglycan cross-links (the number of peptide-stem D-alanines covalently linked to a pentaglycyl bridge) and bridge-links (the number of peptide-stem lysines covalently linked to a pentaglycyl bridge). The concentration of cross-links remained constant in the presence of vancomycin, whereas the number of bridge-links decreased. These changes suggest that vancomycin (at therapeutic levels) interrupts peptidoglycan synthesis in S. aureus by interference with transglycosylation.

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The important anticancer drug Taxol ® (paclitaxel, PTX) owes its unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. The conformation of the microtubule-bound drug has been the focus of numerous research efforts, since the inability of polymerized tubulin to form crystals precludes structure proof by X-ray crystallography. Likewise, although the αβ-tubulin dimer structure has been solved by electron crystallography, the 3.7 Å resolution is too low to permit direct determination of either ligand conformation or binding pose. In this study we present experimental results from 2 H{ 19 F} REDOR NMR that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.