Of the 18 non-cytoplasmic proteins identified, 7 are conserved amongst the proteobacteria and have roles in oxidation/reduction processes. Other conserved proteins are involved in protein Q-VD-Oph in vivo synthesis and turnover (A1W0L1 and A1VYJ3), metabolism (A1VXA8, A1VXB4 and A1VZK9) and ATP synthesis (A1VX18). Of the remaining proteins predicted to be non-cytoplasmic, 3 are structural proteins involved in flagella biosynthesis,
and are unlikely to be involved in cytotoxin biosynthesis or activity. The remaining proteins are predicted to have roles in protein-protein interactions or are involved in binding and transport of lipids (A8FKK7) learn more or cations (A1VXM7). A short list of six potential cytotoxin candidates is summarised in Table 3. PEB3 (A1VY12) was identified in the pool, and this protein has been previously characterised as a glycoprotein and adhesion protein involved in transport of phosphate-containing
molecules . PEB2 (A1VZC6), a major antigenic peptide of C. jejuni on the other hand, is a protein of unknown function which contains a similar signal sequence to PEB3 suggesting similar localisation . It is conserved in C. jejuni and C. coli and BLAST hits return with matches to the accessory colonisation factor protein (acfC) of Vibrio cholerae (34% identical residues/53% positive residues) and a “Conserved Domain Search” find more on NCBI matched to domains involved in extracellular solute binding and transport systems. Based on these inferences, it is unlikely to be the cytotoxin
of interest, although further study of this protein is warranted. Table 3 Short-list of potential cytotoxin candidates identified from LCMS screen of pool B Accession number Full identification name Biological function known or inferred localisation Size (kDa) A1VY12 (cj0289c)* Major antigenic peptide PEB3 Transport Non-cytoplasmic 27.5 A1VZC6 (cj0778) Major antigenic peptide PEB2 Transport Non-cytoplasmic 27.0 A8FLP3 (cj0834c) Putative uncharacterised protein Protein-protein interaction Non-cytoplasmic a(signalP) 46.7 A1W0M3 (cj1240c) Putative periplasmic protein Protein binding Non-cytoplasmic 23.0 A1VZY6 (cj0998c) Putative periplasmic protein Unknown Non-cytoplasmic 20.5 A1VXJ7 (cj0114) Putative periplasmic protein Protein binding Outer membrane 35.4 *Gene designation refers to the best match identified GABA Receptor in Campylobacter jejuni NCTC 11168. a Protein localisation prediction was determined using the program signalP. Prediction of protein localisation was determined using the program PSORTb. Proteins A1W0M3 and A1VZY6 are hypothetical proteins and potential candidates for the cytotoxin, although their predicted sizes (23.0 kDa and 20.5 kDa) are relatively smaller than the high molecular weight cytotoxin previously characterised . One prospective cytotoxin candidate (A1VXJ7), a 315 amino acid residue protein is a TPR family protein which indicates that it is involved in protein:protein interactions (residues 226–265).