Expression and regulation of protein K, an Escherichia coli K1 porin, in Escherichia coli K-12

Purification of MBP-EnvZ fusion proteins using an automated system

Bacteria use two-component signal transduction systems to detect and respond to environmental changes. These systems have been studied systematically in Escherichia coli as a model organism. Most of the signal transduction systems present in E. coli are conserved in related pathogenic bacteria; however, differences in regulation by these systems have been reported from one bacterial species to another [Oropeza, R., and Calva, E. (2009). The cysteine 354 and 277 residues of Salmonella enterica serovar Typhi EnvZ are determinants of autophosphorylation and OmpR phosphorylation. FEMS Microbiol. Lett.292, 282-290]. Our laboratory has been interested in studying the OmpR/EnvZ two-component system in S. enterica. In S. enterica serovar Typhi (Typhi), it regulates the expression of the porin genes, namely ompC, ompF, ompS1, and ompS2. OmpR proteins are identical between E. coli and Typhi, but several differences exist between the EnvZ proteins. To define whether some differences in porin regulation are due to changes on EnvZ, we decided to overexpress and purify E. coli, Typhi, and S. enterica serovar Typhimurium (Typhimurium) EnvZ proteins fused to the maltose-binding protein (MBP) as a purification tag. Differences in the autophosphorylation level of these proteins were evidenced. Hence, considering the differences at the amino acid level between E. coli and Typhi EnvZ proteins, several mutations were introduced in the Typhi EnvZ protein in order to try to find the amino acids affecting the enzymatic activity of the protein. We found that Cys354 plays an important role in defining the enzymatic activity of this histidine kinase. Here, we report the automated purification of a collection of MBP-EnvZ fusions using a mini-chromatography commercial system, but adapting an amylose affinity column packed by ourselves.

Regulation of ompF porin expression by salicylate in Escherichia coli

The expression of ompF, the gene encoding a major outer membrane protein of Escherichia coli, is regulated by various environmental factors. The mechanism by which salicylate (SAL) drastically reduces ompF expression was studied here by means of lacZ fusions to ompF, ompC, and micF, by sodium dodecyl sulfate-gel electrophoresis of outer membrane proteins, and by measurements of outer membrane permeability. Growth of E. coli in LB broth containing SAL strongly reduced ompF-specific translation of an ompF-lacZ fusion. The extent of this reduction varied with the SAL concentration from 64% at 0.5 mM to 95% at 2 mM and greater than 99% at 10 mM. ompF-lacZ transcription was not affected by SAL, whereas ompC-lacZ transcription was elevated by 70%. Since the micF transcript is antisense to a portion of the ompF transcript and is capable of decreasing the translation of ompF, the effect of SAL on micF transcription was measured in a micF-lacZ fusion strain. SAL-grown cells contained three- to fourfold more micF transcript during the logarithmic phase of growth than did the control cultures. However, micF was not absolutely required for the response to SAL. In micF-deleted strains, the effects of SAL on ompF translation, on OmpF in the outer membrane, and on outer membrane permeability were diminished but still evident. The effect of SAL on ompF expression was independent of the osmolarity of the medium and was epistatic to certain ompB regulatory mutations: the high levels of ompF expression found in envZ3 and ompR472 strains were greatly reduced by growth in SAL. Unexpectedly, the OmpC- phenotypes of these mutants were suppressed by SAL. Thus, growth in SAL severely decreases the translation of ompF while enhancing the transcription of micF and ompC. In this respect, SAL-grown cells resemble certain marA and tolC mutants that have high levels of micF and ompC transcripts and low levels of OmpF.