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J. Bacteriol., May 1997, 2857-2862, Vol 179, No. 9
T Yakushi, T Tajima, S Matsuyama and H Tokuda
The major outer membrane lipoprotein (Lpp) of Escherichia coli possesses
serine at position 2, which is thought to function as the outer membrane
sorting signal, and lysine at the C terminus, through which Lpp covalently
associates with peptidoglycan. Arginine (R) is present before the
C-terminal lysine in the wild-type Lpp (LppSK). By replacing serine (S) at
position 2 with aspartate (D), the putative inner membrane sorting signal,
and by deleting lysine (K) at the C terminus, Lpp mutants with a different
residue at either position 2 (LppDK) or the C terminus (LppSR) or both
(LppDR) were constructed. Expression of LppSR and LppDR little affected the
growth of E. coli. In contrast, the number of viable cells immediately
decreased when LppDK was expressed. Prolonged expression of LppDK inhibited
separation of the inner and outer membranes by sucrose density gradient
centrifugation, whereas short-term expression did not. Pulse-labeled LppDK
and LppDR were localized in the inner membrane, indicating that the amino
acid residue at position 2 functions as a sorting signal for the membrane
localization of Lpp. LppDK accumulated in the inner membrane covalently
associated with the peptidoglycan and thus prevented the separation of the
two membranes. Globomycin, an inhibitor of lipoprotein-specific signal
peptidase II, was lethal for E. coli only when Lpp possessed the C-terminal
lysine. Taken together, these results indicate that the inner membrane
accumulation of Lpp per se is not lethal for E. coli. Instead, a covalent
linkage between the inner membrane Lpp having the C-terminal lysine and the
peptidoglycan is lethal for E. coli, presumably due to the disruption of
the cell surface integrity.
Copyright © 1997, American Society for Microbiology
Lethality of the covalent linkage between mislocalized major outer membrane lipoprotein and the peptidoglycan of Escherichia coli
Institute of Molecular and Cellular Biosciences, University of Tokyo, Bunkyo-ku, Japan.
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