Discovery, Evolution, and Application Biological Supramolecular Hosts for Chloride

Chloride is an essential inorganic ion for life. Beyond its role as an electrolyte, chloride mobilization across cellular membranes is known to be involved in a wide range of homeostatic processes including, but not limited to, pH regulation, fluid excretion, and electrical activity. The growing importance of chloride in normal physiology and disease is further evident by recent discoveries of new transporters and biological roles, which have been accelerated through the application of fluorescent biosensors for chloride. The fluorescence imaging of chloride in living cells is linked to our ability to build hosts that can recognize chloride in water, a fundamental challenge in the field of supramolecular chemistry. New advances along these lines remain rare due to the inherent thermodynamic barrier for desolvation of the chloride ion. To address this challenge, we use and evolve Nature to build protein-based hosts for chloride. Even though there are only twenty proteinogenic amino acids, protein sequence space is vast and can be further enriched through protein engineering methods. By selecting for a desired function or property, laboratory-guided evolution allows for this sequence space to be quickly sampled and filtered. For our goal, this approach affords a diverse pool of hosts that can further evolved, characterized, and applied. To this end, I will describe how green fluorescent proteins can serve as platforms to build fluorescent sensors for chloride and, more broadly, serve as biological supramolecular hosts to advance our fundamental understanding of anion recognition in aqueous systems.