Browsing by Subject "Light Signal Transduction"
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Item Multi-Scale Structure and Dynamics of Visual Signaling in Drosophila Photoreceptor Cells(2012-07-16) Helms, Stephen Jess; Ranganathan, RamaA general problem in science today is how to understand complex systems. An emerging and promising approach makes the bold assumption that complex systems adhere to particular design principles. The power of this is that design principles by definition impose an intuitive nature on a system by presupposing purpose. Existing studies have fruitfully shown the application of engineering principles in biology, but biological systems have many distinct features, particularly due to evolution. In this work, I used Drosophila phototransduction, a well-studied sensory system renowned for its high performance, to search for evolutionary design principles. I focused on three levels of structure in the system: compartmentalization of molecules into microvilli, modularity of dynamic scaffolding by InaD, and functional integration within a single domain of InaD. Using rigorous quantitative measurement and theory with an evolutionary mindset, I uncovered intuitive, simplifying design principles at each level: Microvilli are used to build fast, homogeneous signaling compartments whose dimensions are constrained by these requirements. Dynamic scaffolding is a modular feature of InaD PDZs 4-5 which have been co-inherited in many scaffolds. Within PDZ5, ligand binding and oxidation of the domain are linked through pairwise coupling with a conformational equilibrium—a generic property found in all proteins—and not each other. These results show that this approach can be successful in revealing novel design principles in complex evolved systems.Item Photosensing with LOV: Molecular Insights into the Shared Mechanism of Light-Regulated Kinase Signaling between Plant Phototropins and Bacterial Two-Component Systems(2010-01-12) Ko, Wen-Huang; Gardner, Kevin H.With the overall goal of understanding the basis of Light–Oxygen–Voltage (LOV) domain mediated signaling transduction pathways, my graduate research focused on characterizing the role of LOV domains in kinase signaling and the mechanism of signal propagation from LOV domains to a diverse set of downstream effectors. I started from the studies of the LOV domain regulated serine/threonine kinase activity from plant phototropins, later comparing this with LOV domains light–regulated histidine kinases in marine bacteria. Though the plant and bacterial kinases have diverse protein folds and functions, they both share the common photosensing module. Using a combination of biophysical and biochemical techniques, I examined the properties of these light mediated proteins and provided molecular insights in which light signal is transmitted from the core to the surface of the LOV domain. This work also presented detailed biochemical and biophysical characterization of the full–length LOV domain–containing histidine kinase, providing a solid foundation for studying the regulation of the LOV domain in the context of full–length protein. Taken together, I hope to address both the mechanisms that LOV domains use to regulate their effectors, and further how histidine kinases are regulated by their sensory domains. These are the central questions in both the LOV domain and the histidine kinase domain fields, and are of central importance to signal transduction in general.