The crystal structure of a bacterial, bifunctional 5,10 methylene-tetrahydrofolate dehydrogenase cyclohydrolase

The structure of a bifunctional 5,10-methylene-terrahydrofolate dehydrogena se/cyclohyclrolase from Escherichia coli has been determined at 2.5 Angstro m resolution in the absence of bound substrates and compared to the NADP-bo und structure of the homologous enzyme domains from a trifunctional human s ynthetase enzyme. Superposition of these structures allows the identificati on of a highly conserved cluster of basic residues that are appropriately p ositioned to serve as a binding site for the poly-gamma-glutamyl rail of th e tetrahydrofolate substrate. Modeling studies and molecular dynamic simula tions of bound methylene-tetrahydrofolate and NADP shows that this binding site would allow interaction of the nicotinamide and pterin rings in the de hydrogenase active site. Comparison of these enzymes also indicates differe nces between their active sites that might allow the development of inhibit ors specific to the bacterial target.