Dynamic structure of whole cells probed by nuclear Overhauser enhanced nitrogen-15 nuclear magnetic resonance spectroscopy.

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Abstract
The proton-decoupled 15N Fourier transform NMR spectra of 15N-enriched Escherichia coli, Bacillus licheniformis, baker''s yeast [Saccharomyces cerevisiae] and Friend leukemic cells were obtained. The 15N NMR spectra of whole cells displayed 15N resonances originating from protein backbones with lysine, arginine and histidine side chains, RNA, peptidoglycan and phospholipids. Several additional amino and amide resonances were observed but not identified. In bacteria and yeast, the cell wall was the site of a relatively mobile group of molecules, whose resonances dominate the proton-decoupled 15N NMR spectra of whole cells. 15N NMR chemical shifts and nuclear Overhauser effects provided information on the in vivo structure of cell wall peptidoglycan. In Staphylococcus aureus the pentaglycine cross-bridge of cell wall peptidoglycan had a random coil conformation. In B. licheniformis considerable segmental motional freedom was detected in teichuronic acid and peptidoglycan polysaccharide chains in the wall of the intact cell.