Affiliation: | 1. Department of Environmental and Occupational Health, University of Pittsburgh, Pennsylvania;3. Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pennsylvania;4. Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh, Pennsylvania;2. Department of Pediatrics, University of Iowa, Iowa City, Iowa;5. Department of Biochemistry and Protein Crystallography Facility, University of Iowa, Iowa City, Iowa |