Cells have compartments separated by membranes. Many proteins are made in one compartment but actually function in another. The ability of proteins to travel across membranes within cells is essential to cell life. Malfunctions in this process can lead to a variety of inherited and autoimmune diseases in humans. Dr. Mark Paetzel's research focuses on the mechanisms by which proteins travel across cell membranes, a process called protein targeting and translocation. Using the technique of X-ray crystallography, Dr. Paetzel is uncovering the three-dimensional structures of the protein complexes that make up the molecular machines involved in bacterial protein targeting and translocation. A better understanding of the functions and mechanisms of these protein complexes may yield insights about how the process works in human cells. In addition, learning how the process differs between bacteria and human cells could lead to a novel class of antibiotics that can shut down protein targeting and translocation activities in bacteria, but leaves human cells unaffected.