Intellectual Merit: Jumbo phages are very large viruses capable of infecting bacteria. There are many different kinds and they are easy to find, isolate, and grow and play important roles in global ecosystems. This project concerns the relationship between the structures of the protein shells (capsids) of viruses and the sizes of the viral DNAs (genomes) packaged inside them, as well as the evolutionary pathways that lead to viruses of increasing size. Very few structures of jumbo viruses have been determined to date and very little is known about the evolutionary processes that produce their elaborate architectures. Important questions about the evolution of jumbo viruses will be tackled comprehensively by combining cryo-electron microscopy (cryoEM), to investigate the details of capsid architecture, with biochemistry and molecular genetics, to establish their protein and DNA compositions. One hypothesis that will be tested posits that individual mutations in the major capsid protein modify the self-assembly of capsid monomers so as to increase the size of the assembled capsid, allowing additional, superfluous DNA sequences to be packaged, for example, extra copies of some genes. Over time, these unneeded gene copies may be gradually replaced with useful and eventually essential gene sequences, thus locking in the new capsid structure. The studies of virus structural evolution are enabled, on the one hand, by significant improvements in cryoEM technology, and on the other, by advances in sequencing genomic DNA. The two researchers leading this project are experts in these technologies and will work together to address questions not accessible by either approach alone.
Broader Impacts: This project aims at revealing evolutionary connections between the virus capsid and genome by studying structural relationships among very large capsids of different bacterial viruses. In a broader sense, the project will illuminate a regime of macro-molecular complexity that is significantly under-investigated. Bacterial viruses are important model systems for understanding protein structure, self-assembly, and function and are important sources of biotechnology tools (for example, viral promoters, phage display libraries). Structure determination of viral components continues to contribute significantly to the understanding of virus biology and the interactions between host cells and viruses. A complete structural description of the viral subunits, their binding sites and accessible surfaces, will allow exploration of new anti-viral molecules that will be useful medically, in fermentation-based industries, agriculture and in biotechnology including bacterial use for cleaning oil-spills and for generating renewable energy. Education and Outreach opportunities come from the synergy between the two collaborating disciplines and the anticipated impact on undergraduates, graduate students and post-doctoral fellows from the two participating departments, Structural Biology and Biological Sciences. Five students will be recruited each year for this unique training opportunity that includes screening for exceptionally large virions, performing biochemical analyses, and processing cryo-electron microscopy images to visualize capsid structures in three dimensions. Undergraduate recruiting will follow the successful model of the existing "Phage Hunters" program, recruiting from undergraduate classes and through campus chapters of minority-oriented professional organizations (POMS, NSBE). Graduate students involved in the project will gain teaching experience by mentoring undergraduates.
