While humans require the essential amino acid Trp from their diet, plants, fungi, and bacteria have retained the enzymes necessary to synthesize Trp de novo. The five-step pathway starts with the product of the shikimate pathway, chorismate. Chorismate is converted to the aromatic compound anthranilate, which is then conjugated to a phosphoribosyl sugar in the second step of the pathway by anthranilate phosphoribosyltransferase (PAT1). Aside from the characterization of blue-fluorescent trp1 mutants, PAT1 remains to be biochemically investigated. Using steady-state kinetics, the regulation and substrate-specificities of PAT1 from Arabidopsis thaliana and from Citrus sinensis were investigated. Active site mutants were generated to trace the evolution of specificity and regulation in these two enzymes. Because Citrus spp. siphon anthranilate from the Trp pathway and use it for synthesizing defense metabolites, like acridone alkaloids, our findings may explain how plants evolved a pool of anthranilate to use in specialized metabolism.
Support or Funding Information
Williams College and the American Society of Plant Biologists SURF Award
