Arabidopsis 3‐Deoxy‐d‐Arabino‐Heptulosonate 7‐Phosphate (DAHP) Synthases of the Shikimate Pathway Display Both Manganese‐ and Cobalt‐Dependent Activities

ABSTRACT

The plant shikimate pathway directs a significant portion of photosynthetically assimilated carbon into the downstream biosynthetic pathways of aromatic amino acids (AAA) and aromatic natural products. 3‐Deoxy‐

‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase (hereafter DHS) catalyzes the first step of the shikimate pathway, playing a critical role in controlling the carbon flux from central carbon metabolism into the AAA biosynthesis. Previous biochemical studies suggested the presence of manganese‐ and cobalt‐dependent DHS enzymes (DHS‐Mn and DHS‐Co, respectively) in various plant species. Unlike well‐studied DHS‐Mn, however, the identity of DHS‐Co is still unknown. Here, we show that all three DHS isoforms of Arabidopsis thaliana exhibit both DHS‐Mn and DHS‐Co activities in vitro. A phylogenetic analysis of various DHS orthologs and related sequences showed that Arabidopsis 3‐deoxy‐D‐manno‐octulosonate‐8‐phosphate synthase (KDOPS) proteins were closely related to microbial Type I DHSs. Despite their sequence similarity, these Arabidopsis KDOPS proteins showed no DHS activity. Meanwhile, optimization of the DHS assay conditions led to the successful detection of DHS‐Co activity from Arabidopsis DHS recombinant proteins. Compared with DHS‐Mn, DHS‐Co activity displayed the same redox dependency but distinct optimal pH and cofactor sensitivity. Our work provides biochemical evidence that the DHS isoforms of Arabidopsis possess DHS‐Co activity.