The plant hormone ethylene plays important roles throughout growth and development, including regulation of seed germination, seedling growth, leaf and petal abscission, fruit ripening, organ senescence, and pathogen responses. Plants perceive ethylene using membrane-bound receptor proteins. Though the identity of these receptors has been known for some time, the structure of the ethylene-binding domain has thus far evaded characterization. This project will combine computational modeling and experimental characterization to resolve the molecular structure of the ethylene-binding domain. Among the broader impacts is a benefit society based on the agricultural and industrial significance of ethylene, and lay the groundwork for the creation of ethylene nanosensors. A summer art-and-science course will be developed in partnership with a local art center as part of this project; students will engage in art activities that explore the connection between ethylene, ripening, and senescence, thereby allowing students to discover science through art.
Ethylene was the first gaseous hormone discovered and ethylene receptors are present in prokaryotes and plants. The role of ethylene as a signaling molecule has been studied most extensively in plants where it plays important roles throughout growth and development. Ethylene is perceived by membrane-bound receptors, with the ethylene-binding site found within the transmembrane (TM) domains of the receptors. A copper (Cu-I) cofactor is critical for ethylene binding and, based on genetic and biochemical analysis, involves a novel His-His-Cys-Cys binding site for its chelation. This work will integrate a set of experiments, built on a foundation of computational modeling, to solve the structure of the ethylene-binding domain. First, two independent and complimentary computational approaches will be used to model the structure of the ethylene-binding domain: a bottom-up approach using energy-driven sampling of the TM domain, constrained by known characteristics of the binding site; and a top-down approach based on multiple sequence alignments of eukaryotic and prokaryotic ethylene binding domains to predict likely contacting residue pairs. Second, critical features of the ethylene binding domain will be determined by (1) characterizing the ethylene-binding ability of receptor homologues across diverse species and (2) mutational analysis of ethylene receptor function based on predictions of the computational model. Third, based on the computational model, the ethylene-binding domain will be re-engineered as a water-soluble analog to aid in its structural analysis and the creation of ethylene nanosensors. The Broader Impact of the project involves a partnership with AVA Gallery and Art Center (www.avagallery.org/) to develop a two-week summer course ("RIPE!") will be offered to 9-12 year olds each year. Students will engage in projects exploring the connection between ethylene, ripening, and senescence, based around the intuitive awareness of ethylene's role in plants through the popular expression, "One bad apple spoils the whole bunch".
