Folate synthesis in plants: The p-aminobenzoate branch is initiated by a bifunctional PabA-PabB protein that is targeted to plastids

摘要: It is not known how plants synthesize the p-aminobenzoate (PABA) moiety of folates. In Escherichia coli, PABA made from chorismate in two steps. First, PabA and PabB proteins interact to catalyze transfer amide nitrogen glutamine chorismate, forming 4-amino-4-deoxychorismate (ADC). The PabC protein then mediates elimination pyruvate aromatization give PABA. Fungi, actinomycetes, Plasmodium spp. also but have comprising fused domains homologous PabB. These bipartite are commonly called “PABA synthases,” although it unclear whether they produce or ADC. Genomic approaches identified Arabidopsis tomato cDNAs encoding containing domains, plus a putative chloroplast targeting peptide. encode functional enzymes, as demonstrated by complementation an E. coli pabA pabB double mutant yeast PABA-synthase deletant. partially purified recombinant did unless enzyme was added, indicating that forms ADC, behaved monomer size-exclusion chromatography inhibited physiological concentrations PABA, its glucose ester, When peptide GFP expressed protoplasts, fusion appeared only chloroplasts, synthesis plastidial. pericarp fruit, PabA-PabB mRNA level fell drastically ripening advanced, there no fall total content, which stayed between 0.7 2.3 nmol·g-1 fresh weight.