Escherichia coli QueD is a 6-carboxy-5,6,7,8-tetrahydropterin synthase.

To elucidate the early steps required during biosynthesis of a broad class of 7-deazapurine-containing natural products, we have studied the reaction catalyzed by Escherichia coli QueD, a 6-pyruvoyl-5,6,7,8-tetrahydropterin synthase (PTPS) homologue possibly involved in queuosine biosynthesis. While mammalian PTPS homologues convert 7,8-dihydroneopterin triphosphate (H(2)NTP) to 6-pyruvoyltetrahydropterin (PPH(4)) in biopterin biosynthesis, E. coli QueD catalyzes the conversion of H(2)NTP to 6-carboxy-5,6,7,8-tetrahydropterin (CPH(4)). E. coli QueD can also convert PPH(4) and sepiapterin to CPH(4), allowing a mechanism to be proposed.