Modern drug discovery programs require the contribution of researchers in a number of specialist areas. One of these areas is structural biology. Using X-ray crystallography, the molecular basis of how a drug binds to its biological target and exerts its mode of action can be defined. For example, a drug that binds into the active site of an enzyme can inhibit its important biological function and stop the enzyme from working. By understanding this molecular interaction in fine detail, researchers can begin to design new compounds with a view to developing drugs with improved properties, such as better activity and safety. One example of how X-ray crystallography is employed in drug discovery is highlighted in a research project currently underway at the University of Adelaide. A multidisciplinary team of researchers has identified a new class of antibiotics to combat infections caused by pathogenic bacteria, such as "Staphylococcus aureus," the agent responsible for golden staph. Many of the medicines commonly used to treat these infections have become ineffective due to the development of drug resistance. This article describes how the research team is focused on a completely new molecular target in the bacterial cell, Biotin protein ligase (BPL). BPL is an essential metabolic enzyme so inhibitors of this protein should also be effective at preventing the growth of the bacteria. Currently, none of the antibiotics in clinical use exert their activity through this enzyme, so BPL inhibitors represent a completely new class of antibiotic. The article discusses the drug discovery process and the role that structural biology played in that process. It concludes with suggested classroom activities and a list of online resources.