Rhodopsin is a visual protein found in the rods of the eye's retina, and is an archetype for the broad class of membrane proteins known as G-protein-coupled receptors (GPCRs). With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Michael Brown from the University of Arizona to explore how the interactions of this protein with lipids in membranes and with water control the visual signaling process. Although the atomic structures of proteins, including rhodopsin, are now known, the correspondence to their actions in lipid membranes remains an open question. This project combines experiment and theory to study how the flow of water into the protein affects the activation of rhodopsin within a cellular membrane environment. In addition, the project provides specialized training in the chemistry of membrane proteins and lipids to graduate students and postdoctoral fellows as well as undergraduate and high-school students. The new fundamental knowledge is disseminated not only through the published scientific literature, but also through workshops developed with the Arizona Flandreau Science Center. The project is further integrated with an outreach program involving Arizona's Science, Engineering, and Math Scholars program, focusing on promising students who are first in their family to attend college, from low-income households, and women and minorities. The work involves international collaborations and affords opportunities aimed at integrating and promoting human cooperation and global education. This research project characterizes important interactions involving membrane lipids and water that control the light activation of rhodopsin in the catalytic G-protein cycle of visual signaling. Because activation is a pH-dependent process, whether water goes into or out of the protein is crucial to the actual chemistry of the reaction mechanism. The project combines molecular spectroscopy with scattering methods through a synergetic interplay of experiment and theory. The research is intended to illuminate the hydration-mediated activation mechanism of rhodopsin, and explores how the membrane soft matter comprising lipids and water affects the process. Hydrophilic polymer osmolytes of low specificity are used to quantify the influx of water into the protein together with gravimetric methods, and reveal the influences of water on the activation of rhodopsin and its interactions with the cognate G-protein transducin. The project further addresses how the membrane lipids govern rhodopsin function in the cellular environment through the bilayer properties and interactions. The information from this study is intended to contribute new insights into the fundamental chemistry of the membrane components that are likely to govern G-protein-mediated biological signaling at the cellular level. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.