Dihydrofolate reductase is a housekeeping enzyme which is responsible for maintaining the amount of tetrahydrofolate in the cell. It catalyzes the NADPH-linked reduction of 7,8-dihydrofolate to 5,6,7,8- tetrahydrofolate. Tetrahydrofolate is the cofactor used in synthesis of several important metabolites like thymidylate, a building block of DNA. Crystal Structure of Dihydrofolate Reductase from Yersinia pestis was solved at 1.55A resolution. Protein has single domain composed of 4 alpha helices and 8 beta-sheets.