Structure and Dynamics of Pentaglycyl Bridges in the Cell Walls of Staphylococcus aureus by 13C−15N REDOR NMR

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Abstract
Whole cells and cell-wall fractions of Staphylococcus aureus have been labeled by various combinations of [1-13C]glycine, [15N]glycine, l-[6-13C]lysine, l-[6-15N]lysine, d-[1-13C]alanine, and d-[15N]alanine. The resulting materials have been examined using 13C and 15N solid-state, magic-angle spinning NMR techniques including cross-polarization, double cross-polarization, and rotational-echo double resonance. The results of these measurements indicate that the peptidoglycan glycyl bridges are complete (five units long) and form cross-links between three-quarters of all peptide stems. The pentaglycyl bridges are immobilized in lyophilized cell-wall fractions in a compact conformation with inter-residue spacings comparable to those of an α helix. The bridges have a similar compact conformation in intact whole cells, regardless of whether the cells have been lyophilized or were hydrated and frozen at −10 °C. The bridges are also in a time-averaged compact conformation in whole cells at 0 °C but with sizable structural fluctuations associated with local mobility. A small fraction of bridges are in extended-chain conformations.