Pterin binding enzymes. This family includes dihydropteroate synthase (DHPS) and cobalamin-dependent methyltransferases such as methyltetrahydrofolate, corrinoid iron-sulfur protein methyltransferase (MeTr) and methionine synthase (MetH). DHPS, a functional homodimer, catalyzes the condensation of p-aminobenzoic acid (pABA) in the de novo biosynthesis of folate, which is an essential cofactor in both nucleic acid and protein biosynthesis. Prokaryotes (and some lower eukaryotes) must synthesize folate de novo, while higher eukaryotes are able to utilize dietary folate and therefore lack DHPS. Sulfonamide drugs, which are substrate analogs of pABA, target DHPS. Cobalamin-dependent methyltransferases catalyze the transfer of a methyl group via a methyl- cob(III)amide intermediate. These include MeTr, a functional heterodimer, and the folate binding domain of MetH.
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