Campylobacter jejuni is one of the leading causes of acute gastroenteritis in the developed world. The serine peptidase Cj0511, homologous to C-terminal processing peptidases, has been shown to be required for optimum virulence in its influences towards biofilm formation, stress tolerance and pancreatic amylase triggered α-dextran secretion. There is also the implication that Cj0511 may be involved in host protein degradation during infection, given it is a component of secreted outer membrane vesicles. Extensive characterisation of this protein has to date been lacking, with our previous indirect attempts via quantitative proteomic and degradomic analysis of wild-type C. jejuni and a Cj0511 knock-out (Δcj0511) failing to find identify putative endogenous protein targets against a background of elevated proteolytic activity in its absence.
Here we chose to take a direct approach by characterising the cleavage specificity of recombinant Cj0511, using N-terminal amine isotopic labelling of substrates (N-TAILS). On a defined substrate of B-casein we show that Cj0511 possesses distinct proteolytic activity. Putative native substrates of Cj0511 were also identified through analysis of differential proteolytic activity between treated and untreated C. jejuni whole cell lysates derived from Δcj0511.