(A–C) 13C-13C NMR spectra of whole cells (A), cell envelopes (B), and (U-13C,15N)-labeled PagL-containing proteoliposomes (C). Characteristic crosspeaks of Ala, Ser, and Thr residues of PagL, and endogenous E. coli lipids (Lip) are indicated. Reprinted with permission from (53). To see this figure in color, go online.