Our lab is interested in studying the structure and function of membrane proteins. Membranes surrounding cells protect the cell from the environment. They are highly impermeable to most polar molecules, which prevents the contents of the cell from escaping and toxins from entering. At the same time, the cells need to take up nutrients, release waste, and adjust the ion concentrations inside. ABC transporters are the most common protein machinery that pumps a variety of substrates across membranes. As some ABC proteins are related to severe diseases such as cancer, cystic fibrosis, and immune deficiency, insights of the transport mechanism will have significant impact in biology and medicine. Our recent studies of the bacterial maltose transporter show that one part of the pump opens and closes like a pair of tweezers. This motion explains how ATP is used to do the mechanical work of translocation. We are also pursuing crystallographic studies of several viral proteins that facilitate viral entry and packaging. The group of viruses we are studying includes Dengue, Yellow Fever, West Nile, and SARS-coronavirus.