Discovery of novel motilin antagonists: Conversion of tetrapeptide leads to orally available peptidomimetics

A hemolytic-uremic syndrome-associated strain O113:H21 Shiga toxin-producing Escherichia coli specifically expresses a transcriptional module containing dicA and is related to gene network dysregulation in Caco-2 cells

Shiga toxin-producing (Stx) Escherichia coli (STEC) O113:H21 strains are associated with human diarrhea and some of these strains may cause hemolytic uremic syndrome (HUS). The molecular mechanism underlying this capacity and the differential host cell response to HUS-causing strains are not yet completely understood. In Brazil O113:H21 strains are commonly found in cattle but, so far, were not isolated from HUS patients. Here we conducted comparative gene co-expression network (GCN) analyses of two O113:H21 STEC strains: EH41, reference strain, isolated from HUS patient in Australia, and Ec472/01, isolated from cattle feces in Brazil. These strains were cultured in fresh or in Caco-2 cell conditioned media. GCN analyses were also accomplished for cultured Caco-2 cells exposed to EH41 or Ec472/01. Differential transcriptome profiles for EH41 and Ec472/01 were not significantly changed by exposure to fresh or Caco-2 conditioned media. Conversely, global gene expression comparison of both strains cultured in conditioned medium revealed a gene set exclusively expressed in EH41, which includes the dicA putative virulence factor regulator. Network analysis showed that this set of genes constitutes an EH41 specific transcriptional module. PCR analysis in Ec472/01 and in other 10 Brazilian cattle-isolated STEC strains revealed absence of dicA in all these strains. The GCNs of Caco-2 cells exposed to EH41 or to Ec472/01 presented a major transcriptional module containing many hubs related to inflammatory response that was not found in the GCN of control cells. Moreover, EH41 seems to cause gene network dysregulation in Caco-2 as evidenced by the large number of genes with high positive and negative covariance interactions. EH41 grows slowly than Ec472/01 when cultured in Caco-2 conditioned medium and fitness-related genes are hypoexpressed in that strain. Therefore, EH41 virulence may be derived from its capacity for dysregulating enterocyte genome functioning and its enhanced enteric survival due to slow growth.

CD8+ T-cell recognition of a synthetic epitope formed by t-butyl modification

We set out to clone Bax-specific CD8+ T-cells from peripheral blood samples of primary chronic lymphocytic leukemia patients. A number of clones were generated using a Bax peptide pool and their T-cell epitope was mapped to two peptides sharing a common 9-aa sequence (LLSYFGTPT), restricted by HLA-A*0201. However, when these T-cell clones were tested against highly purified syntheses (>95%) of the same peptide sequence, there was no functional response. Subsequent mass spectrometric analysis and HPLC fractionation suggested that the active component in the original crude peptide preparations (77% pure) was a peptide with a tert-butyl (tBu) modification of the tyrosine residue. This was confirmed by modification of the inactive wild type (wt) sequence to generate functionally active peptides. Computer modeling of peptide:HLA-A*0201 structures predicted that the tBu modification would not affect interactions between peptide residues and the HLA binding site. However these models did predict that the tBu modification of tyrosine would result in an extension of the side chain out of the peptide-binding groove up towards the TCR. This modified product formed <1% of the original P603 crude peptide preparation and <0.05% of the original 23 peptide mixture used for T-cell stimulation. The data presented here, illustrates the potential for chemical modifications to change the immunogenicity of synthetic peptides, and highlights the exquisite capacity of TCR to discriminate between structurally similar peptide sequences. Furthermore this study highlights potential pitfalls associated with the use of synthetic peptides for the monitoring and modulating of human immune responses. This article is protected by copyright. All rights reserved.