David Barford is a structural biologist who has made fundamental contributions to understanding how the activity of proteins is controlled. His work has had a particular impact in the study of the cell cycle, the sequence of events leading to chromosome duplication and cell division, which is often disrupted in cancer. Enzymes regulate the activity of other proteins by adding or removing phosphate groups. As a young scientist, David conducted award-winning work on the structures of several key enzymes that either phosphorylate or dephosphorylate proteins — all major players in the pathways that underlie the cell’s metabolism and reproduction. Some of these enzymes are defective in cancer and have since been developed as therapeutic targets for cancers such as melanoma. More recently, David has used X-ray crystallography and cryo-electron microscopy to solve the structure of the multiprotein anaphase-promoting complex (APC/C), which labels proteins for destruction as the chromosomes separate before division.