Figure 3.

(a) ¹³C{¹⁵N}REDOR of whole cells of E. faecalis labeled with l-[1-¹³C]Ala and l-[ε-¹⁵N]Lys at 4.8 ms dipolar evolution grown in absence (left) and presence of vancomycin at 10 μg/mL (right). ¹³C{¹⁵N}REDOR spectra of VRE grown in vancomycin concentrations of 0 and 20 μg/mL are results of 75248 and 320000 accumulated scans respectively. The magic angle spinning was at 5000 Hz. (b) Enlarged overlaid S₀ and ΔS spectra centered at 174 ppm for VRE grown with vancomycin (red), and without (black). ΔS 174-ppm peak intensity, which was directly proportional to the bridge-link density, was independent of induction of vancomycin resistance in VRE. (c) ¹³C{¹⁵N}REDOR dephasings (ΔS/S₀) of alanyl-carboxyl carbon at 174 ppm. Solid line is the calculated REDOR dephasing curve for two ¹³Cs in l-[1-¹³C]Ala-l-[1-¹³C]Ala bridge that are dephased by the ¹⁵N of l-[ε-¹⁵N]Lys with ¹³C-¹⁵N distances of 1.3 and 3.3 Å (dotted lines). ¹³C{¹⁵N}REDOR dephasing is highly selective for the PG-bridge structure, as demonstrated by the calculated dephasing curve for ¹³C-¹⁵N distances corresponding to 2.0 and 4.0 Å (red curve), which does not fit observed dephasings.