1. C- and O-glycosidic bond formation with PRPP
C- and O-glycosidic bond formation with PRPP. The phosphoribosyl donor PRPP is shown in red, and atoms derived from PRPP in the intermediates and products are also shown in red.
C- and O-glycosidic bond formation with PRPP. The phosphoribosyl donor PRPP is shown in red, and atoms derived from PRPP in the intermediates and products are also shown in red. (A) Biosynthesis of tetrahydromethanopterin. Compound labels: l, 4-hydroxybenzoate; m, 5′-phospho-β-d-ribosyl 4-hydroxybenzene; n, 5′-phospho-β-d-ribosyl 4-aminobenzene; o, N-[(7,8-dihydropterin-6-yl)methyl]-4-(1-deoxy-d-ribulosyl)aminobenzene; p, 1-(4-{N-[(7,8-dihydropterin-6-yl)methyl]amino}phenyl)-5-(5-phospho-α-d-ribulosyl)-1-deoxyribitol. Enzyme 1, 4-aminobenzoate phosphoribosyltransferase (5-phospho-α-d-ribose 1-diphosphate:4-aminobenzoate 5-phospho-β-d-ribofuranosyltransferase [decarboxylating], EC ); enzyme 2, 1-(4-{N-[(7,8-dihydropterin-6-yl)methyl]amino}phenyl)-5-(5-phospho-α-d-ribulosyl)-1-deoxyribitol synthase. This enzyme activity has not been identified. The four reactions leading from compound m to compound n in effect convert a hydroxy group to an amino group and involve the formation of phosphate ester and the addition of an aspartyl residue and the removal of Pi and fumarate (304). The three reactions leading from compound n to compound o involve the attachment of a pterin derivative (R = N-[7,8-dihydropterin-6-yl]methyl) to the nitrogen of compound n followed by opening of the ribosyl moiety and isomerization to a ribulose derivative and dephosphorylation to form compound o. The boxed compound is the product of the pathway for 5,6,7,8-tetrahydromethanopterin (with a complete structure of the pteridyl moiety), the active cofactor in transformation of carbon dioxide to methane in methanogenic Archaea (301), and is formed from compound p by attachment of a glutamyl moiety to the phosphate group followed by dehydrogenation of the pteridyl moiety. (B) Biosynthesis of arabinosyl monophosphodecaprenol. Compound labels: q, decaprenyl phosphate; r, 5-phospho-β-d-ribosyl 1-O-monophosphodecaprenol (decaprenylphospho-β-d-ribosyl 5-phosphate). Enzyme 3, decaprenyl phosphate phosphoribosyltransferase (5-phospho-α-d-ribosyl 1-diphosphate:decaprenyl-phosphate 5-phosphoribosyltransferase; EC ). The boxed compound is the arabinosyl donor arabinosyl monophosphodecaprenol, which is formed from compound r by dephosphorylation of the ester at C-5 of the ribosyl moiety followed by epimerization. The latter two reactions occur outside the cell (5). (C) Biosynthesis of butirosin. Compound labels: s, neamine; t, 5″-phosphoribostamycin. Enzyme 4, neamine phosphoribosyltransferase. The boxed compound is butirosin. Two isomers are synthesized; one contains a ribosyl moiety (shown) and a second contains an arabinosyl moiety (not shown). Other aminoglycoside antibiotics derived from neamine, i.e., neomycin B, paromomycin, and lividomycin B, lack the 4-amino-2-hydroxybutyryl side chain but contain an N-acetylaminoglucosyl moiety attached to C-3″ of the ribosyl moiety, and the pseudodisaccharides of the three compounds are differently decorated with hydroxyl and amino groups (318).
Bjarne Hove-Jensen et al. Microbiol. Mol. Biol. Rev. 2017; doi: /MMBR