Catalyzes the condensation of para-aminobenzoate (pABA) with 6-hydroxymethyl-7,8-dihydropterin diphosphate (DHPt-PP) to form 7,8-dihydropteroate, the immediate precursor of folate derivatives. Is the target for the sulfonamide group of antimicrobial drugs. Sulfonamide drugs act as pABA analogs, they inhibit the reaction by acting as alternative substrates, leading to a 'dead end' sulfa-pterin product. (7,8-dihydropterin-6-yl)methyl diphosphate + 4-aminobenzoate = 7,8-dihydropteroate + diphosphate Is potently inhibited by sulfonamides, with Ki values between 25 nM and 850 nM. Cofactor biosynthesis; tetrahydrofolate biosynthesis; 7,8-dihydrofolate from 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine diphosphate and 4-aminobenzoate: step 1/2. Homodimer. Reaction proceeds via an ordered binding mechanism, with DHPPP binding to the enzyme first, inducing a structural change which forms the pABA-binding site. One or two residue insertions within this gene are responsible for sulfonamide resistance in streptococcal clinical isolates. Sulfonamide-resistance mutations in the second loop region have a drastic effect on pABA binding. Belongs to the DHPS family.