6-hydroxymethyl-7,8-dihydropterin + ATP = (7,8-dihydropterin-6-yl)methyl diphosphate + AMP + H(+) GTP + H2O = 7,8-dihydroneopterin 3'-triphosphate + formate + H(+) Cofactor biosynthesis; 7,8-dihydroneopterin triphosphate biosynthesis; 7,8-dihydroneopterin triphosphate from GTP: step 1/1. Cofactor biosynthesis; tetrahydrofolate biosynthesis; 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine diphosphate from 7,8-dihydroneopterin triphosphate: step 4/4. Homomer. In the N-terminal section; belongs to the HPPK family. In the C-terminal section; belongs to the GTP cyclohydrolase I family.