FIG 4.

Cu impairs lipoprotein biogenesis and activates Cpx through NlpE. (A) Cultures were serially diluted on LB agar and LB agar supplemented with 4 mM CuCl₂. (B) Cultures were grown in the presence of 3 mM CuSO₄ to mid-log phase, and levels of cpxP mRNA were measured. Samples were prepared and analyzed together with samples presented in Fig. 3, the DMSO control presented is the same here as in Fig. 3 Data are means ± standard errors of the means. (C) Relative LacZ levels in ΔnlpE cells harboring a PcpxP-lacZ transcriptional reporter and overproducing plasmid-borne NlpE variants targeted to the OM. Data are means ± standard deviations. (D) Cultures were grown to mid-log phase in the presence (Cu +) or absence (Cu −) of 3 mM CuCl₂. Lgt and Lnt replete (+) or deplete (−) samples were obtained by growing strains PAP9403 and KA472 in the presence or absence of arabinose; LspA activity was inhibited by treating cells with Glb (LspA −) in comparison to mock treatment (LspA +). Protein samples were taken and probed for Lpp by immunoblotting. Diacyl form Lpp is noted as +2. Lpp forms with signal peptides attached are noted as +SP. Peptidoglycan-bound Lpp forms are noted as * and **. See text for details.