Evolutionary biochemistry of pentameric ligand-gated ion channels

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At its most basic level our nervous system is an intricate circuit of specialized cells called neurons that communicate with each other using electrical signals. This process relies on proteins embedded in the neuronal membrane, called ion channels, whose activity both generates and propagates these electrical signals. Billions of years of evolution have led to a staggering array of ion channel diversity, with different ion channel types opening and closing in response to a variety of stimuli.Ligand-gated ion channels, which open upon binding small chemical ligands, are Nature's ultimate molecular sensors. They convert chemical signals into electrical impulses by coupling the binding of small molecules to the opening of a membrane-spanning ion conducting pore. The short-term goal of my new research program is to understand mechanisms of ligand-gated ion channel function. In the long-term, this insight will be used to guide the engineering of ligand-gated ion channels with unique chemical specificities. These ligand-gated ion channel-based “biosensors” will be genetically encoded, meaning that can be seamlessly integrated into future cell-based therapeutic and diagnostic systems.Our ability to engineer ligand-gated ion channel biosensors is limited by current gaps in our understanding of channel structure, function, and mechanism. To uncover the structural and mechanistic basis of enigmatic ligand-gated ion channel functions, the proposed research, which will be carried out by a team of graduate and undergraduate students, will couple a new and innovative evolutionary biochemistry approach to single molecule biophysical experiments. The evolutionary biochemistry approach involves charting the evolutionary history of proteins, in order to trace the changes in amino acid sequence that gave rise to modern day protein functions. The amino acid sequences of ancestral ligand-gated ion channels are reconstructed so that these ancestral channels can be “resurrected” and characterized at the single molecule level. This new and emerging approach represents a rational way of exploring ligand-gated ion channel amino acid sequences, in order to illuminate structure-function relationships that have stymied conventional approaches. The result will be a better understanding of fundamental aspects of ligand-gated ion channel structure and function, which will open the door to designing channels with unique properties for use as chemical biosensors. These genetically encoded biosensors will have broad diagnostic, therapeutic and industrial applications, leading to socio-economic benefits for Canadians.