Alternative pathways in directed evolution

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Proposal Number: 1402101Institution: Johns Hopkins UniversityP.I.: Ostermeier, Marc A. Title: Alternative pathways in directed evolutionThe study of evolution is important, not only because it is central to biology, but also because researchers apply evolution in the laboratory to develop beneficial proteins and cells for use in in many areas including human health, detection of chemical and biological agents, and remediation of toxic compounds in the environment. This proposal seeks to evaluate a fundamentally new approach for applying evolution in the laboratory. Paradoxically, the goal is to first develop proteins that are worse at performing the desired function and then re-engineering these to be improved in function. The approach is based on a growing appreciation in evolutionary biology of the complexity of proteins and that sometimes a set of changes to a protein that have a negative effect on protein function in isolation, can have a positive effect when combined. Success of this project would impact the fields of evolutionary biology and biotechnology. Potentially, this new approach could lead to proteins and cells with superior properties that could not be readily created using existing methods. The project will also train a pre-doctoral and undergraduate student in research.The objectives are (1) to evaluate fundamentally different directed evolution selection strategies for evolving proteins away from local fitness peaks towards other distant fitness peaks and (2) to address shortcomings in our understanding of evolutionary processes in fluctuating environments (i.e. evolution under variable selection). The TEM-15 beta-lactamase allele will be subjected to directed evolution under a variety of selective pressure schemes designed to traverse the fitness landscape in different ways. These schemes include (1) positive selection, (2) neutral drift, (3) retrogressive selection, (4) oscillating selection, and (5) fluctuating antibiotic environments. This evolution will exploit our band-pass gene circuit that allows the selection of beta-lactamase alleles at any desired fitness level (e.g. away from genes with lower or higher fitness). The progress and outcomes of evolution will be monitored by deep sequencing, which will determine the identity and distribution of mutations for each selection mechanism. The interpretation of mutational trajectories and outcomes will be aided by the comprehensive determination of the effect of individual mutations in TEM-15.Due to the interdisciplinary nature of the project, this award by the Biotechnology, Biochemical, and Biomass Engineering Program of the CBET Division is co-funded by the Systems and Synthetic Biology Program of the Division of Molecular and Cellular Biology.