Disulphide bond formation is a critical step in the folding of multiple bacterial virulence proteins such as fimbrial adhesins, toxins and the secretion systems. Most bacteria contain the classic Dsb system for disulphide catalysis, consisting of an oxidative (DsbA/DsbB) and an isomerase (DsbC/DsbD) pathway. However, many pathogens encode an extended arsenal of thiol oxidation pathways.
In addition to the classic Dsb system, the human pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) contains a DsbL/I redox pair and a plasmid encoded DsbA homologue SrgA, to catalyse the oxidative folding of secreted virulence factors. Additionally, we have shown that Salmonella has a Dsb related Scs system, which confers copper tolerance, a critical trait for the survival of this pathogen. A recent bioinformatics analysis identified an additional Dsb-like protein in Salmonella called BcfH. This protein is encoded in the highly prevalent and conserved bcf fimbrial operon, which is involved in S. Typhimurium adhesion and persistence within the host.
To gain a better understanding of the role of BcfH in the assembly and the stability of the bcf fimbrial components and its contribution in the pathogenesis of Salmonella, we have carried out a detailed structural and functional characterisation of this protein. Using a combination of biochemical and biophysical approaches, we have shown that BcfH is a dimeric DsbA like protein that functions as both a disulphide oxidase and isomerase. Furthermore, we have investigated the structural properties of this protein by Small-angle X-ray scattering (SAXS) and X-ray crystallography. We are also working towards identifying the potential substrates for BcfH.
Taken together, our data have revealed that Salmonella has complex thiol-disulphide redox pathways dedicated to assembling virulence proteins and providing fitness traits such as copper tolerance, all critical for the infectivity and survival of this pathogen. Characterizing these systems is increasing our molecular understanding of the virulence pathways in Salmonella as well as other Gram-negative pathogens that contain a similar redox machineries.
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