inhibitor (or immunity protein) of the contact-dependent growth inhibition (CDI) system of Burkholderia pseudomallei E479, 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 Burkholderia pseudomallei E479 (which is a tRNase). 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. Although related B. pseudomallei E479 CdiA-CT has structural homology to B. pseudomallei 1026B CdiA-CT (both tRNases), their cognate CdiI immunity proteins share no significant sequence or structure homology. This CdiI binds its cognate toxin CdiA-CT domain with high affinity.