We are involved in projects to determine the atomic structures of macromolecular complexes and membrane proteins using X-ray diffraction. Our work on ATP synthase, in collaboration with Sir John Walker (MRC Mitochondrial Biology Unit) aims to determine the structure of this energy-transducing complex from mitochondria. It is a complex structure of sixteen different polypeptides with a total molecular weight of over 500,000 Da. We have determined the structure of the catalytic sector (F1-ATPase) in a variety of different states. The structures of an F1c10 subcomplex of the yeast ATP synthase, a three-subunit complex of the peripheral stalk, and the NMR structure of another component of the peripheral stalk (the OSCP protein), have been assembled within a cryo-EM derived envelope to provide a model of the whole enzyme. We are now focusing on obtaining high quality crystals of the complete enzyme. We hope that the structure will help us to understand the mechanism that couples proton transport to ATP synthesis.