Project Summary/Abstract Infectious diseases are the second leading cause of death in the world. With novel classes of antibiotic drugs virtually nonexistent, and the resistance of pathogenic bacteria to current ones increasing rapidly, the develop- ment of new approaches is becoming an imperative for advancing human health efforts. Molecular modeling will play an essential role in these new approaches, due to the fundamentally atomic-scale nature of the critical structures, processes, and interactions underlying the function of both bacterial proteins and antibacterial agents. In order to illuminate these structures and processes, the PI will focus on a defining feature of Gram-negative bacteria, namely their second, outer membrane, and how integral membrane proteins are inserted there. These outer-membrane proteins (OMPs), practically all of which belong to a specific class known as -barrels, utilize two key systems for insertion: the BAM system, essential for viability, and the related TAM system, necessary for virulence. Exploiting these systems as antibacterial targets requires a comprehensive understanding of the relationship between structure, dynamics, and function. In the first aim, a novel mechanism in which the key component of each system, BamA and TamA, respectively, catalyzes insertion through augmentation of its own -barrel will be evaluated. Intermediate states of insertion will be generated in molecular dynamics simulations and assayed experimentally through both disulfide cross-linking and electrophysiology measurements. In the second aim, how BamA and TamA perturb the membrane, itself an active participant in the insertion process, will be determined. Simulations have indicated the existence of a membrane defect that forms due to an unusually thin and unstable part of the -barrel of BamA; mutations to alter this perturbation, and presumably decrease OMP insertion efficiency, will be predicted in silico and tested in vivo. Finally, in the third aim, the dynamics of BamA and TamA as well as BamA's interactions with other BAM components will be characterized. Based on the conformational changes observed, small-molecule drug candidates will be selected that limit conformational flexibility and/or inhibit binding of BamA or TamA to other complex members. These candidates will then be tested experimentally for antibacterial activity.