Glutamate-adding enzyme which catalyzes the binding of the first glutamyl side chain to dihydropteroate. Leads to the de nove synthesis of tetrahydrofolate. de novo (By similarity). 7,8-dihydropteroate + ATP + L-glutamate = 7,8-dihydrofolate + ADP + H(+) + phosphate Cofactor biosynthesis; tetrahydrofolylpolyglutamate biosynthesis. Belongs to the folylpolyglutamate synthase family.