This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. SAXS solution scattering data will be used for image processing of electron microscopy data on bacterial adhesion pili. Research in my lab currently focuses on two bacterial adhesion pili, CFA/I pili and P-pili. Both of these pili are helical filaments, approximately 8nm in diameter with variable lengths on the order of 1micron. The role of adhesion pili for bacteria is to bind, and remain bound, to the human host cell, thereby allowing bacterial colonization and subsequent disease. CFA/I pili are expressed on enterotoxigenic E. coli that cause Traveler¿s Diarrhea when they colonize the small intestines. P-pili are expressed on E. coli that cause Urinary Tract Infections that involve the kidneys. Our studies elucidate how the structure of each pilus type facilitates survival of the bacteria in their specialized host environment. For example, we have shown that P-pili can unwind their helix, extending to 5 times their original length. We propose this prevents their breaking and detaching from the urinary tract during periodic fluid flow. Our current goal is to determine the structural basis of CFA/I pili¿s ability to remain bound to the small intestines, a truly harsh environment due to the acidic conditions and peristalsis the bacteria must survive in the stomach, and the reversal back to neutral pH and scissor-like contractions that are encountered upon entering the small intestine. We currently have three-dimensional helical reconstructions of both CFA/I pili and P-pili. Studies on the P-pili are further advanced, with a 9.8 ¿ resolution structure from electron cryomicroscopy data. For CFA/I pili, we are just about to begin collecting cryo data, and the current reconstruction is at 14.5 ¿ from negatively stained samples. Concurrently, a collaborator is working on developing a pili-based vaccine against Traveler¿s Diarrhea (Capt. Stephen Savarino; Naval Medical Research Center).