LIGAND-INDUCED DISTORTION OF AN ACTIVE-SITE IN THYMIDYLATE SYNTHASE UPON BINDING ANTICANCER DRUG 1843U89

The anticancer drug 1843U89 inhibits thymidylate synthase (TS) at sub- nanomolar concentrations and is undergoing clinical trial. The 1.95 An gstrom crystal structure of Escherichia coli TS bound to the drug and dUMP reveals that the 1843U89 binding surface includes a hydrophobic p atch that is normally buried. To reach this patch, 1843U89 inserts int o the wall of the TS active site, resulting in a severe local distorti on of the protein. In this new conformation, active-site groups that n ormally bind to the catalytic cofactor methylenetetrahydrofolate inste ad bind to 1843U89 in new ways. This structure provides a rare example of a protein that can bind tightly to distinct substances using a sin gle, flexible, binding surface. This has implications for drug design, as 1843U89 could not have been obtained from current structure-based approaches.