Most species of the genus
Bifidobacterium
contain the gene cluster PFNA, which is presumably involved in the species-specific communication between bacteria and their hosts. The gene cluster PFNA consists of five genes including
fn3
, which codes for a protein containing two fibronectin type III domains. Each fibronectin domain contains sites similar to cytokine-binding sites of human receptors. Based on this finding we assumed that this protein would bind specifically to human cytokines
in vitro
. We cloned a fragment of the
fn3
gene (1503 bp; 501 aa) containing two fibronectin domains, from the strain
B. longum
subsp.
longum
GT15. After cloning the fragment into the expression vector pET16b and expressing it in
E. coli
, the protein product was purified to a homogenous state for further analysis. Using the immunoferment method, we tested the purified fragment’s ability to bind the following human cytokines: IL-1β, IL-6, IL-10, TNFα. We developed a sandwich ELISA system to detect any specific interactions between the purified protein and any of the studied cytokines. We found that the purified protein fragment only binds to TNFα.
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