To identify proteins with a potential role in the interaction of Bifidobacterium longum with intestinal epithelial cells, we profiled the protein response of B. longum NCC2705 following interaction with Caco-2 cells. Thirty-one protein spots, belonging to a total of 23 proteins, which exhibited a change in abundance of at least 3-fold were identified in B. longum NCC2705 following co-culture with Caco-2 cells, and were subsequently identified. Changes in expression were confirmed at the transcriptional level for a selection of these proteins. Enolase (Eno) and elongation factor Tu (EF-Tu) were amongst the proteins that showed the most prominent increase in abundance. Interaction of these proteins with plasminogen (Plg) was analyzed by Plg overlay assays, glutathione S-transferase (GST)-pull down, and western blot analysis. The results suggested that EF-Tu and Eno serve as surface receptors for B. longum NCC2705 binding to human plasminogen. Purified GST-EF-Tu and GST-Eno inhibited adhesion of B. longum NCC2705 to Caco-2 cells. Collectively, our data suggest that Eno and EF-Tu moonlight as adhesions, and are possibly involved in the protective role played by B. longum NCC2705 in defense against enteric pathogens. Biological significance The interaction of bifidobacteria with the human host plasminogen/plasmin system confirms the existence of a new component in the molecular cross-talk between bacteria and the host. Our study analyzed proteins EF-Tu and Eno with Plg binding activity, and they can inhibit adhesion of B. longum NCC2705 to Caco-2 cells, suggesting their role in the bacterial adherent to the enterocyte surface.
Keywords: Adhesion; Bifidobacterium; EF-Tu; Enolase; Plasminogen.
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