Frequency, magnitude, and mechanisms of collateral fitness effects of mutations

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A complete understanding of the effects of mutations is important for understanding biology and the treatment of disease. Deleterious mutations are generally understood to cause negative effects by disrupting what the mutated protein was originally supposed to do. However, the deleterious effects of mutations might also arise from causing the mutated protein to do things it should not do, such as interfere with unrelated biological process. These are known as collateral effects. Very little is known about the extent to which mutations cause deleterious effects by the latter mechanism. In this research, the investigators will comprehensively quantify the collateral effects of mutations in two antibiotic resistance proteins and uncover mechanisms for the mutational effects. This will contribute to the understanding of how proteins evolve and the mechanisms by which mutations can affect the physiology of the cell, which is important for understanding normal biological function as well as human disease and the evolution of antibiotic resistance. Each year of this research, two graduate students, two undergraduates, and one high school student will be trained in research. The graduate students will attend scientific conferences to present their research and gain mentorship experience supervising the undergraduate and high school students. Collateral fitness effects of mutations are those effects which do not derive from changes in the ability of the gene/protein to perform its physiological functions. The contribution of collateral fitness effects of mutations to protein evolution is unknown. In this research, collateral fitness effects of all single missense mutations and all single-codon insertion/deletion mutations in two antibiotic resistance proteins will be measured using a combination of large scale mutagenesis, growth competition, and deep sequencing technology. The data will also be used to identify mutations to test hypotheses of the mechanisms behind collateral fitness effects. For example, since protein evolution rates anti-correlate with protein expression levels, one possibility is that deleterious collateral fitness effects occur when mutations cause the protein to misfold or misinteract with other proteins. Very little is known about the frequency, magnitude, and mechanisms of collateral fitness effects, but such information is critical for understanding the distribution and origins of fitness effects of mutations and interpreting the rates of protein evolution. The systematic and comprehensive study of such effects in two proteins will generate a wealth of data from which to understand the contribution of collateral fitness effects to the distribution of fitness effects of mutations and to protein evolution rates.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.