Increased efficiency of the outer membrane PhoE protein pore in escherichia coli K-12 mutants with heptose-deficient lipopolysaccharide

Abstract

The pore properties of PhoE protein channels in the outer membrane of a lipoprotein-deficient mutant and in a mutant with heptose-deficient lipopolysaecharide were investigated. The absence of lipoprotein neither affects the rate of permeation of glucose 6-phosphate or of the/~-lactam antibiotic eephsulodin through the PhoE pore nor the inhibition of cephsulodin permeation by polyphosphate. In contrast, heptose deficiency results in a 6-to 8-fold increase in the rates of permeation of glucose 6-phosphate and cephsulodin. Possible explanations for these data are discussed. It is argued that the lipopolysaecharide structure synthesized under phosphate limitation may be similar to that of the heptoseless mutant and hence that not only the structure of the PhoE protein pore but also the structure of the lipopolysaecharide may promote the uptake of Pi and Pi-containing solutes under phosphate limitation.

Endotoxins: Relationships between Structure, Function, and Activity

“…The effective channel diameter of the porin trimers was only slightly influenced by the lipid matrices [38][39][40]. Therefore, a question can be answered, raised by Korteland and Lugtenberg [42], whether (i) an increased pore diameter, (ii) an increased amount of open pores or (iii) the absence of sterical hindrance by the sugar and the loss of negatively charged phosphate groups, leading to reduced charged repulsion, is responsible for the increased uptake of charged substrates by PhoE in Re mutants as compared to wildtype strains. From the abovementioned data, it is obvious, that in Re mutants neither the pore diameter changes nor the amount of open pores increases and therefore, the reduced charge repulsion is the most likely.…”

Pore Formation and Function of Phosphoporin PhoE of Escherichia coli Are Determined by the Core Sugar Moiety of Lipopolysaccharide

“…A reduction of the stability of the LPS layer might do one of the following: (i) allow pore formation by porins already inserted into the PL side or (ii) influence the stability of the entire membrane and thus facilitate insertion and pore formation. The former possibility seems to be unlikely, because lower amounts of PhoE (10,32) and other outer membrane proteins (11) have been found in Re mutants than in wild-type bacteria, indicating that these proteins do not insert into the membrane.…”