Folate-binding triggers the activation of folylpolyglutamate synthetase

Folic acid is an essential vitamin for normal cell growth, primarily throug h its central role in one-carbon metabolism. Folate analogs (antifolates) a re targeted at the same reactions and are widely used as therapeutic drugs for cancer and bacterial infections. Effective retention of folates in cell s and the efficacy of antifolate drugs both depend upon the addition of a p olyglutamate tail to the folate or antifolate molecule by the enzyme folylp olyglutamate synthetase (FPGS). The reaction mechanism involves the ATP-dep endent activation of the free carboxylate group on the folate molecule to g ive an acyl phosphate intermediate, followed by attack by the incoming L-gl utamate substrate. FPGS shares a number of structural and mechanistic detai ls with the bacterial cell wall ligases MurD, MurE and Muff, and these enzy mes, along with FPGS, form a subfamily of the ADP-forming amide bond ligase family. High-resolution crystallographic analyses of binary and ternary co mplexes of Lactobacillus casei FPGS reveal that binding of the first substr ate (ATP) is not sufficient to generate an active enzyme. However, binding of folate as the second substrate triggers a large conformational change th at activates FPGS and allows the enzyme to adopt a form that is then able t o bind the third substrate, L-glutamate, and effect the addition of a polyg lutamate tail to the folate. (C) 2001 Academic Press.