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J. Biol. Chem., Vol. 277, Issue 37, 34247-34253, September 13, 2002
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From the The lipid matrix of the outer membrane of
Gram-negative bacteria is an asymmetric bilayer composed
of a phospholipid inner leaflet and a lipopolysaccharide outer leaflet.
Incorporated into this lipid matrix are, among other macromolecules,
the porins, which have a sieve-like function for the transport or
exclusion of hydrophilic substances. It is known that a reduced amount
of porins is found in the outer membrane of rough mutants as compared with wild-type bacteria. This observation was discussed to be caused by
a reduced number of insertion sites in the former. We performed
electrical measurements on reconstituted planar bilayers composed of lipopolysaccharide on one side and a phospholipid mixture
on the other side using lipopolysaccharide from various rough mutant
strains of Salmonella enterica serovar Minnesota. We found
that pore formation by PhoE trimers that were added to the
phospholipid side of the bilayers increased with the increasing length
of the lipopolysaccharide core sugar moiety. These results allow us to
conclude that the length of the sugar moiety of lipopolysaccharide is
the parameter governing pore formation and that no particular insertion
sites are required. Furthermore, we found that the voltage gating of
the porin channels is strongly dependent on the composition of the
lipid matrix.
Research Center Borstel, Center for Medicine
and Biosciences, Department of Immunochemistry and Biochemical
Microbiology, Parkallee 1-40, D-23845 Borstel, Germany and the
§ Department of Molecular Cell Biology, Institute for
Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The
Netherlands
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