Colicin Immunity Protein

Immunity proteins against Colicins are produced by E. coli alongside the relevant colicin protein to protect the cell from the cytotoxic domain of the colicin. Usually this involves binding to and blocking the active site of the domain, to prevent it from targeting the cells own mechanisms.

Once released from the producing cell, the immunity proteins are no longer needed, as the cytotoxic domain needs to be active once a target cell has been penetrated. Often it is disassociated from the colicin upon binding to an outer membrane receptor on the target cell.