Engineering Designed Proteins for Light Capture, Energy Transfer, and Emissive Sensing In Vivo

Joshua A Mancini, University of Pennsylvania


Proteins that are used for photosynthetic light harvesting and biological signaling are critical to life. These types of proteins act as scaffolds that hold small, sometimes metal-containing organic molecules in precise locations for light absorption and successive use. For signaling proteins, this energy can be used to induce a photoisomerization of the small molecule that can turn on or off a signaling cascade that controls the physiology of an organism. Alternatively, photosynthetic light-harvesting proteins funnel this energy in a directional manner towards a charge separating catalytic component that can change this light energy into chemical energy. The protein environment also serves to tune the photophysical properties of the small molecules. This is seen extensively with the linear tetrapyrroles that are used in both photosynthetic and signaling proteins. Many efforts have been made to harness these natural proteins for societal use, including improving photophysical properties and interfacing capabilities with manmade catalytic components. Several methods of achieving improvement have entailed structurally guided mutation and directed evolution. However, these methods all have their limitations due to the inherent complexity and fragility of the natural proteins. This work presents an alternative more robust method to natural proteins. My thesis states: that man-made proteins, known as maquettes, employing basic rules of protein folding, can be designed to become light harvesting and signaling proteins that can be assembled fully in vivo providing an alternative, robust, and versatile platform for meeting the diverse array of societal “green chemistry” and biomedical needs. This in vivo assembly is carried out by interacting with cyanobacterial protein and pigment machinery, both as stand-alone units and as protein fusions with natural antenna complexes. Additionally, this work offers insight for fast and tight binding of circular and linear tetrapyrroles to the maquettes both in vitro and in vivo. Design principles are also established for increasing the amount of linear tetrapyrrole attachment to the maquette as well as modulating their photophysical properties. Fast and tight binding of cofactors, high cofactor attachment yields, and control of cofactor photophysical properties are all prerequisites for the maquettes to be successful in vivo photosynthetic light harvesting and signaling proteins.

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Recommended Citation

Mancini, Joshua A, "Engineering Designed Proteins for Light Capture, Energy Transfer, and Emissive Sensing In Vivo" (2017). Dissertations available from ProQuest. AAI10264747.