inhibitor (or immunity protein) of the contact-dependent growth inhibition (CDI) system of Cupriavidus taiwanensis CdiI immunity protein and similar proteins
CDI toxins are expressed by gram-negative bacteria as part of a mechanism to inhibit the growth of neighboring cells. This model represents the inhibitor (CdiI, also called CdiI immunity protein) of the CdiA effector protein from Cupriavidus taiwanensis, and similar proteins. CdiA secretion is dependent on the outer membrane protein CdiB. Upon binding to a receptor on the surface of target bacteria, the CDI toxin is delivered via its C-terminal domain (CdiA-CT). The CdiI immunity proteins are intracellular proteins that inactivate the toxin/effector protein to prevent auto-inhibition. They are specific for their cognate CdiA-CT and do not protect cells from the toxins of other CDI+ bacteria. Thus, CDI systems encode a complex network of toxin-immunity protein pairs that are deployed for intercellular competition. This C. taiwanensis CdiI is alpha-helical and binds its cognate toxin CdiA-CT domain with high affinity.