When directed evolution is combined with deep sequencing, it becomes possible to track changes in frequency of thousands of protein variants simultaneously in a single experiment. Known as deep mutational scanning, the sequence-fitness landscape of a protein can now be experimentally determined. The Procko lab uses directed evolution of transmembrane proteins in mammalian cells to determine the phenotypic fitness of many thousands of amino acid substitutions. From this unprecedented mutational data, it is possible to map ligand binding sites to conserved regions in the sequence and infer putative conformational states. The lab is applying this technology to problems under two general themes: chemokine receptors in the immune system, and small molecule receptors and transporters in the nervous system. There is an emphasis on using the data for biomedical purposes, including mapping drug interaction sites and engineering new transmembrane proteins with altered properties.