The human cytochrome P450 (P450) enzymes are monooxygenases involved in the metabolism of steroid hormones, pharmaceuticals, carcinogens, and fat-soluble vitamins. P450 enzymes therefore have many direct impacts on human health. The study of P450 enzymes has led to several important advances in medicine including new therapies and the safer use of existing therapies. One important, yet understudied family of human P450 enzymes is the 27 family including P450 27A1, 27B1, and 27C1. These enzymes catalyze the oxidations of several important lipophilic hormones including vitamin D derivatives (27A1 and 27B1), cholesterol derivatives (27A1), and retinoids (27C1). The products of these reactions can have either positive or negative effects on human health depending on their concentrations in the body. Therefore, it could be valuable to either increase or decrease these enzymes’ activities for clinical therapies. This research project focuses on how the structure of the enzymes determines their function. In particular, we are interested in how the interactions between the P450 enzymes and the redox partner protein adrenodoxin can alter enzyme structure and in turn P450 function. We are also interested in the development of uncompetitive drug therapies that can act more selectively to prevent enzyme activity by altering enzyme structure. We propose that a thorough mechanistic description of the P450 27 family structure-function relationship will inform the development of new and safer therapies involving these enzymes and various cancers, hormone regulation, and bone health. The focus on lipophilic hormones is in line with the overall vision of the laboratory examining the function of other membrane-associated, lipid-active enzymes for the sake of developing new clinical therapies. Over the next five years, the goals of the laboratory include applying structural approaches novel to the study of P450 enzymes like small-angle X-ray scattering and small-angle neutron scattering, applying classic structural approaches to P450 enzymes like X- ray crystallography, determining the effects adrenodoxin has on P450 function, and testing the ability of known P450 27A1 inhibitors to act in an uncompetitive manner. To accomplish these goals, we will expand our laboratory personnel while maintaining a focus on undergraduate research training. In total, the laboratory seeks to improve human health by increasing our basic understanding of enzyme function and by working to embrace diversity in training the next generation of biomedical scientists.