Connecting structure and fitness landscapes to overcome antibiotic resistance

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Project summary - Connecting structure and fitness landscapes to overcome antibiotic resistance Antibiotic resistance is a pressing, multifaceted challenge. Pathogen evolution is outstripping the supply of new compounds and analogues, threatening a global health crisis. New approaches to understand adaptation are clearly necessary, but this is a difficult problem. The mechanisms of resistance are often unknown, as well as the overall combination of changes that produce overall microbial fitness changes. Technical developments in high-throughput biochemistry have allowed massive variant libraries to be assayed, which opens the door to constructing predictive models of resistance, but these have until our recent work ignored complex mutations, specifically insertions and deletions, which play a massive role by producing major changes to underlying fitness landscapes with small mutations. To study how, we will combine experimental evolution, deep mutational scanning, and multitemperature crystallography to produce an integrated model for how insertions and deletions permit rapid changes to protein function. We will use the Streptogramin A family as our model antibiotic. These are ribosome-targeting compounds produced by Streptomyces. Resistance occurs through Vat proteins, which specifically inactivate Streptogramin A (SA) via acetylation. A collaboration with the Seiple lab at UCSF has led to a modular synthesis of SA that allows variants to be simply produced, as well as several novel compounds with demonstrated reduced acetylation in vitro. We will determine how adaptation to these novel compounds proceeds, and how indels within a key variable substrate-binding loop modulate it. In my first aim, I will use experimental evolution to uncover how Vat proteins adapt to streptogramins, and how the addition of insertions and deletions within this loop change the adaptive potential. In my second aim, I will conduct high-throughput stability measurements to determine the mechanistic basis for resistance changes, and then use deep mutational scanning to measure the mutational accessibility and biophysical basis for an evolved adaptive trajectory. In my third aim, I will use cryo- and multitemperature crystallography to determine the static and dynamic basis for indel-potentiated changes to substrate specificity towards new SAs. The completion of these aims will produce an integrated picture of microbial adaptation and essential new insight into how complex but understudied mutations radically shift the adaptive potential of genes. The cross- disciplinary nature of the project will expose me to a number of techniques and approaches that will provide me with excellent training opportunities under the mentorship of field-defining experts. The new frameworks and techniques I will develop will help establish my scientific maturity as I pursue my goal of an independent research position studying the mechanistic basis of molecular protein evolution at a university.