The objective is to document the process of membrane channel formation using two representative atomic resolution snapshots, corresponding to CytA protoxin, a bacterial channel-forming Bt delta-endotoxin, and its membrane-inserted form. To this end, X-ray crystallography will be carried out to determine the atomic resolution structures of protoxin Cyt A and the membrane-inserted Cyt A, which will be crystallized in detergent-lipid micelles based on an established strategy developed for alpha-hemolysin crystallization. A direct comparison of these two structures will reveal protein conformational changes that underlie a variety of intriguing transmembrane active processes, including membrane insertion of globular proteins by proteolytic activation and formation of ion conductivity and selectivity in a membrane ion-conducting channel. In addition to the value of intellectual interests, Bt toxins are extremely toxic to the larvae of several important pests in agriculture, yet totally harmless to human. The Cyt A structures will therefore help design biological pesticides, which will be the a major alternative to chemical pesticides with an expectation of reducing environmental pollution due to chemical spaying. Even more alarming is the fact that all pests will show some degree of resistance to chemical pesticides; finding an alternative to chemical pesticides is imperative.
