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J Biol Chem, Vol. 275, Issue 7, 4687-4692, February 18, 2000
From the Division of Cell Biology and Biophysics, School of
Biological Sciences, University of Missouri-Kansas City,
Kansas City, Missouri 64110
As part of the membrane attack complex complement
protein C9 is responsible for direct killing of bacteria. Here we show
that in the periplasmic space of an Escherichia coli cell
C9 is converted from a protoxin to a toxin by periplasmic conditions
missing in spheroplasts. This conversion is independent of the pathway
by which C9 enters the periplasm. Both, C9 shocked into the periplasm and plasmid-expressed C9 targeted to the periplasm via a
signal sequence are toxic. Toxicity requires disulfide-linked C9
because export into the periplasm of cells defective in disulfide bond synthesis (dsbA and dsbB mutants) is not toxic
unless N-acetylcysteine is added externally to promote
cystines. A N-terminal fragment, C9[1-144], is not toxic nor is
cytoplasmically expressed C9, even in trxB mutants that are
able to form disulfide bonds in the cytoplasm. Importantly, expression
of full-length C9 in complement-resistant cells has no effect on their
viability. Expression and translocation into the periplasm may provide
a novel model to identify molecular mechanisms of other bactericidal
disulfide-linked proteins and to investigate the nature of bacterial
complement resistance.
Molecular Aspects of Complement-mediated Bacterial Killing
PERIPLASMIC CONVERSION OF C9 FROM A PROTOXIN TO A TOXIN*
,
*
This work was supported by University of Missouri Research
Board Grant 1598, by National Institutes of Health Grants AI19478 and
GM53748, and by a Marion Merrell Dow Professorship Endowment (to
A. F. E.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Dept. of Cell Biology, Neurobiology, and Anatomy,
Medical College of Wisconsin, Milwaukee, WI 53226.
§
To whom correspondence should be addressed. Tel.: 816-235-5316;
Fax: 816-235-1503; E-mail: essera@umkc.edu.
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