Grant: Operating Grant

Living cells are perturbed by "osmosis", the flow of water into or out of cells in response to changes in the osmotic pressure of their environment. Cells must sense and respond to this osmotic stress because hydration changes perturb many cellular processes, threatening survival and growth. When faced with dehydration, cells take up benign compounds called osmolytes, water follows and cell functions resume. Transporters are protein molecules with dimensions of nanometers that function as pumps to select specific chemicals and move them into or out of cells. We were the first to show that a single protein, osmosensory transporter ProP of bacterium Escherichia coli, could detect changes in osmotic pressure and respond by transporting osmolytes into the cell. Our work suggests that the rate at which ProP pumps osmolytes depends on the osmotic pressure because ProP, itself, must be correctly hydrated to function effectively. We will test that hypothesis by probing the structure and transport mechanism of ProP, thereby determining how they are altered by osmotic pressure changes. Exploiting our current structural model for ProP, we will experimentally modify ProP structure, determine what steps in the transport process are affected by the osmotic pressure and monitor interactions of electromagnetic radiation with ProP to determine how its structure changes over time (its structural dynamics). Our work is important to human health because osmoregulation promotes the survival and health of disease-causing bacteria. Osmoregulation is also critical for the survival and health of human cells, particularly those in the kidneys and the brain. Many biological principles are universal, so knowledged gained through the study of bacterial protein ProP will help us to understand the functions of corresponding proteins in other organisms, including humans.