A rapid selective extraction procedure for the outer membrane protein (OmpF) from Escherichia coli

Outer membrane protein C is a protective and unique vaccine antigen against Shigella flexneri 3a

The anti-Shigella vaccine is one of the WHO's top priorities. Every year the disease kills more than 200,000 people worldwide and poses a serious threat to children under 5 years of age and the elderly. Increasing antibiotic resistance and limitations in diagnostics emphasize the need to develop an effective vaccine. Recent research and clinical trials report multiple approaches used in Shigella-vaccine development. However, despite the efforts of researchers, pharmaceutical companies and health care organizations, there is no licensed vaccine against shigellosis available to the community. Here, we expressed, broadly characterized and demonstrated the protective properties of outer membrane protein C as an effective molecule serving as a universal antigen for Shigella vaccine. Most of the current approaches to the development of Shigella vaccine are based on the polysaccharide antigens, which are serotype specific and have always been challenging in terms of their high specificity, targeting the most exposed surface antigens identified for certain Shigella serotypes. Here, we confirm immunogenic and protective properties of the recombinant OmpC protein, which protects mice against a lethal dose of a virulent strain 2 weeks after active immunization.

Cyclic OmpC peptidic epitope conjugated to tetanus toxoid as a potential vaccine candidate against shigellosis

In earlier works we have described that mice immunized with outer membrane protein OmpC survive the challenge with live Shigella flexnerii 3a. We have also identified conformational epitope of this protein, that was recognized by mice antibodies. The aim of current work was to investigate whether synthetic OmpC epitope homologs can elicit immunological response sufficient in protecting mice against shigellosis. Several linear peptides containing RYDERY motif were synthesized and conjugated to poly-lysine. These conjugates appeared to be poor immunogens and to boost the immunological response an addition of the adjuvant (MPL) was required. Unfortunately, the MPL alone caused a very high immunological reaction that was masking response to peptidic epitope. Under those circumstances we used tetanus toxoid (TT) as the carrier protein for the peptides and the agent stimulating immunological response. Series of cyclic peptides, homologs of the OmpC main epitope were synthesized and conjugated to TT. The loop size in cyclic peptides varied by number of glycine residues, i.e., 1-3 residues added to the GLNRYDERYIGK motif. The linear GLNRYDERYIGC-TT was also prepared as the control. The latter conjugate gave the highest immunological response, followed by the cyclic-GGLNRYDERYIGC-TT and cyclic-GLNRYDERYIGC-TT. The third peptide, cyclic-GGGLNRYDERYIGC-TT, gave a very low response, although it was the most resistant to proteolysis. However, antibodies obtained against cyclic-GGLNRYDERYIGC-TT were more potent to recognize both OmpC and Shigella flexnerii 3a cells than the antibodies against linear GLNRYDERYIGC-TT. Furthermore, the monoclonal antibodies raised against linear GLNRYDERYIGC-TT showed 20-fold lower dissociation constant (KD) than the naturally occurring polyclonal antibodies from umbilical cord sera. Monoclonal antibodies also gave a weaker signal in electron microscope than mice and human polyclonal antibodies. In overall, our results point to cyclic peptides as better candidates for a vaccine development, since they are eliciting production of the higher affinity antibodies against Shigella cells and OmpC.

Layer-by-layer Assembled Membranes with Immobilized Porins

With the synthesis and functionalization of membranes for selective separations, reactivity, and stimuli responsive behavior arises new and advanced opportunities. The integration of bio-based channels is one of these advancements in membrane technologies. By a layer-by-layer (LbL) assembly of polyelectrolytes, outer membrane protein F trimers (OmpF) or "porins" from Escherichia coli with a central pore of ~2 nm diameter at its opening and ~0.7 × 1.1 nm at its constricted region are immobilized within the pores of poly(vinylidene fluoride) microfiltration membranes, as opposed to traditional ruptured lipid bilayer or vesicles processes. These OmpF-membranes demonstrate selective rejections of non-charged organics over ionic solutes, allowing the passage of salts up to 2 times higher than traditional nanofiltration membranes starting with rejections of 84% for 0.4-1.0 kDa organics. The presence of charged groups in OmpF membranes also leads to pH-dependent salt rejection through Donnan exclusion. These OmpF-membranes also show exceptional durability and stability, delivering consistent and constant permeability and recovery for over 160 h of operation. Characterization of solutions containing OmpF, and membranes were conducted during each stage of the process, including detection by fluorescence labelling (FITC), zeta potential, pH responsiveness, flux changes, and rejections of organic-inorganic solutions.

Shigella flexneri 3a outer membrane protein C epitope is recognized by human umbilical cord sera and associated with protective activity

Shigella flexneri 3a is one of the five major strains of the Shigella genus responsible for dysentery, especially among children, in regions of high poverty and poor sanitation. The outer membrane proteins (OMP) of this bacterium elicit immunological responses and are considered a prime target for vaccine development. When injected into mice they elicit a protective immunological response against a lethal dose of the pathogen. The OMPs from S. flexneri 3a were isolated and resolved by two-dimension-SDS-PAGE. Two 38-kDa spots were of particular interest since in our earlier studies OMPs of such molecular mass were found to interact with umbilical cord sera. These two spots were identified as OmpC by ESI-MS/MS spectrometry. By DNA sequencing, the ompC gene from S. flexneri 3a was identical to ompC from S. flexneri 2a [Gene Bank: 24113600]. A 3D model of OmpC was built and used to predict B-cell type (discontinuous) antigenic epitopes. Six epitopes bearing the highest score were selected and the corresponding peptides were synthesized. Only the peptides representing loop V of OmpC reacted strongly with the umbilical cord serum immunoglobulins. To determine which amino acids are essential for the antigenic activity of the epitope, the loop V was scanned with a series of dodecapeptides. The peptide RYDERY was identified as a minimal sequence for the loop V epitope. Truncation at either the C- or N-terminus rendered this peptide inactive. Apart from C-terminal tyrosine, substitution of each of the remaining five amino acids with glycine, led to a precipitous loss of immunological activity. This peptide may serve as a ligand in affinity chromatography of OmpC-specific antibodies and as a component of a vaccine designed to boost human immune defenses against enterobacterial infections.

Characterization of Pores Formed by YaeT (Omp85) from Escherichia coli

Proteins of the Omp85 family play a major role in the biogenesis of the bacterial outer membrane, since they were shown to mediate insertion of outer membrane proteins. The Escherichia coli Omp85 homologue YaeT is essential for viability, but its exact mode of action is not yet elucidated. We could show that YaeT is composed of two distinct domains, an amino-terminal periplasmic and a carboxy-terminal membrane domain. The full length YaeT and the isolated membrane domain induce pores when reconstituted in planar lipid membranes. The pores exhibit a certain variability of conductance indicating a flexible structure, which could be an essential property of a lateral opening channel releasing proteins into the bacterial outer membrane. We could further show that the periplasmic domain proves to be essential for in vivo function of YaeT.