Our lab is interested in structure-function studies of ATP-binding-cassette (ABC) transporters, also known as traffic ATPases. ABC transporters are the most common protein machineries that pump a variety of substrates across biological membranes. As some ABC proteins are related to severe diseases such as cancer, cystic fibrosis, and macular degeneration, insights of the transport mechanism will have significant impact in biology and medicine. We use both biochemical methods and X-ray crystallography to elucidate the mechanism of the bacteria maltose transporter. We also study the class II viral membrane fusion mechanism. Recent structural and biochemical studies of the flavi- and alphavirus have revealed a new class of viral fusion proteins (class II), that are significantly different from the class I viral fusion proteins represented by influenza hemagglutinin (HA). We are pursuing crystallographic studies of the class II viral fusion proteins at their low-pH-induced fusion-active states.