Molecular Cloning and Characterization of ATP-Phosphoribosyl Transferase from Arabidopsis, a Key Enzyme in the Histidine Biosynthetic Pathway

摘要

Wehave characterized two isoforms of ATP-phosphoribosyl transferase(ATP-PRT) from Arabidopsis (AtATP-PRT1 [accession no.AB025251] and AtATP-PRT2), catalyzing the first step ofthe pathway of hisidine (His) biosynthesis. The primary structuresdeduced from AtATP-PRT1 and AtATP-PRT2cDNAs share an overall amino acid identity of 74.6% and containN-terminal chloroplast transit peptide sequences. DNA-blot analysesindicated that the ATP-PRTs in Arabidopsis are encoded by two separategenes with a closely similar gene structural organization. Both genetranscripts were detected throughout development, and protein-blotanalysis revealed predominant accumulation of the AtATP-PRT proteins inArabidopsis leaves. The His auxotrophy of a his1 mutantof Saccharomyces cerevisiae was suppressed by thetransformation with AtATP-PRT1 andAtATP-PRT2 cDNAs, indicating that both isoforms arefunctionally active ATP-PRT enzymes. The Kmvalues for ATP and phosphoribosyl pyrophosphate of the recombinantAtATP-PRT proteins were comparable to those of the native ATP-PRTs fromhigher plants and bacteria. It was demonstrated that the recombinantAtATP-PRTs were inhibited by l-His (50% inhibition ofinitial activity = 40–320 μm), suggesting that Hisbiosynthesis was regulated in plants through feedback inhibition byl-His.