Various bacterial toxins have potent insecticidal activity. Recently, the Toxin 
complexes (Tc's) of Photorhabdus and Xenorhabdus species have become an 
increased focus of current research. These large tripartite toxins with 
molecular masses >1.4 megadaltons consist of three components termed A, B, and C 
(or TcA, TcB, and TcC). While TcA is involved in receptor binding and toxin 
translocation, TcC possesses the specific toxin enzyme activity and TcB is a 
linker between components TcA and TcC. Here, a structure function analysis of 
the toxins is described and the application of Tc toxins as potential 
insecticides is discussed.