Comparative properties of three pteridine reductases

Enzymatic and Mutational Analysis of the PruA Pteridine Reductase Required for Pterin-Dependent Control of Biofilm Formation in Agrobacterium tumefaciens

Pterins are ubiquitous biomolecules with diverse functions including roles as cofactors, pigments, and redox mediators. Recently, a novel pterin-dependent signaling pathway that controls biofilm formation was identified in the plant pathogen, Agrobacterium tumefaciens A key player in this pathway is a pteridine reductase termed PruA, where its enzymatic activity has been shown to control surface attachment and limit biofilm formation. Here, we biochemically characterize PruA to investigate the catalytic properties and substrate specificity of this pteridine reductase. PruA demonstrates maximal catalytic efficiency with dihydrobiopterin and comparable activities with the stereoisomers dihydromonapterin and dihydroneopterin. Since A. tumefaciens does not synthesize or utilize biopterins, the likely physiological substrate is dihydromonapterin or dihydroneopterin, or both. Notably, PruA does not exhibit pteridine reductase activity with dihydrofolate or fully oxidized pterins. Site-directed mutagenesis studies of a conserved tyrosine residue, the key component of a putative catalytic triad, indicate that this tyrosine is not directly involved in PruA catalysis but may be important for substrate or cofactor binding. Additionally, mutagenesis of the arginine residue in the N-terminal TGX3RXG motif significantly reduces the catalytic efficiency of PruA, supporting its proposed role in pterin binding and catalysis. Finally, we report the enzymatic characterization of PruA homologs from Pseudomonas aeruginosa and Brucella abortus, thus expanding the roles and potential significance of pteridine reductases in diverse bacteria.Importance Biofilms are complex multicellular communities that are formed by diverse bacteria. In the plant pathogen, Agrobacterium tumefaciens, the transition from a free-living motile state to a non-motile biofilm state is governed by a novel signaling pathway involving small molecules called pterins. The involvement of pterins in biofilm formation is unexpected and prompts many questions about the molecular details of this pathway. This work biochemically characterizes the PruA pteridine reductase involved in the signaling pathway to reveal its enzymatic properties and substrate preference, thus providing important insight into pterin biosynthesis and its role in A. tumefaciens biofilm control. Additionally, the enzymatic characteristics of related pteridine reductases from mammalian pathogens are examined to uncover potential roles of these enzymes in other bacteria.

Characterization of quinonoid-dihydropteridine reductase (QDPR) from the lower eukaryote Leishmania major

Biopterin is required for growth of the protozoan parasite Leishmania and is salvaged from the host through the activities of a novel biopterin transporter (BT1) and broad-spectrum pteridine reductase (PTR1). Here we characterize Leishmania major quinonoid-dihydropteridine reductase (LmQDPR), the key enzyme required for regeneration and maintenance of H(4)biopterin pools. LmQDPR shows good homology to metazoan quinonoid-dihydropteridine reductase and conservation of domains implicated in catalysis and regulation. Unlike other organisms, LmQDPR is encoded by a tandemly repeated array of 8-9 copies containing LmQDPR plus two other genes. QDPR mRNA and enzymatic activity were expressed at similar levels throughout the infectious cycle. The pH optima, kinetic properties, and substrate specificity of purified LmQDPR were found to be similar to that of other qDPRs, although it lacked significant activity for non-quinonoid pteridines. These and other data suggest that LmQDPR is unlikely to encode the dihydrobiopterin reductase activity (PTR2) described previously. Similarly LmQDPR is not inhibited by a series of antifolates showing anti-leishmanial activity beyond that attributable to dihydrofolate reductase or PTR1 inhibition. qDPR activity was found in crude lysates of Trypanosoma brucei and Trypanosoma cruzi, further emphasizing the importance of H(4)biopterin throughout this family of human parasites.