Bisubstrate analogue inhibitors of 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase: Synthesis and biochemical and crystallographic studies

6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the tr ansfer of pyrophosphate from ATP to 6-hydroxymethyl-7,8-dihydropterin (HP), leading to the biosynthesis of folate cofactors. Like other enzymes in the folate pathway, HPPK is an ideal target for the development of antimicrobi al agents because the enzyme is essential for microorganisms but is absent from human and animals. Three bisubstrate analogues have been synthesized f or HPPK and characterized by biochemical and X-ray crystallographic analyse s. All three bisubstrate analogues consist of a pterin, an adenosine moiety , and a link composed of 2-4 phosphoryl groups. P-1-(6-Hydroxymethylpterin) -P-2-(5 ' -adenosyl)diphosphate (HP(2)A, 5) shows little affinity and inhib itory activity for E. coli HPPK, P-1-(6-Hydroxymethylpterin)-P-4-(5 ' -aden osyl)triphosphate (H(P)3A, 6) shows moderate affinity and inhibitory activi ty with K-d = 4.25 muM in the presence of Mg2+ and IC50 = 1.27 muM. P-1-(6- Hydroxymethylpterin)-P-4-(5 ' -adenosyl)tetraphosphate (HP(4)A, 7) shows th e highest affinity and inhibitory activity with K-d = 0.47 muM in the prese nce of Mg2+ and IC50 = 0.44 muM The affinity of MgHP(4)A for HPPK is simila r to 116 and 76 times higher than that of MgADP and 6-hydroxymethylpterin, respectively. The crystal structure of HPPK in complex with 7 (HPPK MgHP4A) has been determined at 1.85 Angstrom resolution with a crystallographic R factor of 0.185. The crystal structure shows that 7 occupies both HP- and A TP-binding sites and induces significant conformational changes in HPPK. Th e biochemical and structural studies of the bisubstrate analogues indicate that the bisubstrate analogue approach can produce more potent inhibitors f or HPPK and the minimum length of the link for a bisubstrate analogue is si milar to7 Angstrom.