Structural insights into the dual substrate specificities of mammalian and Dictyostelium dihydropteridine reductases toward two stereoisomers of quinonoid dihydrobiopterin

AbstractUp to now, d-threo-tetrahydrobiopterin (DH4, dictyopterin) was detected only in Dictyostelium discoideum, while the isomer l-erythro-tetrahydrobioterin (BH4) is common in mammals. To elucidate the mechanism of DH4 regeneration by D. discoideum dihydropteridine reductase (DicDHPR), we have determined the crystal structure of DicDHPR complexed with NAD+ at 2.16Å resolution. Significant structural differences from mammalian DHPRs are found around the coenzyme binding site, resulting in a higher Km value for NADH (Km=46.51±0.4μM) than mammals. In addition, we have found that rat DHPR as well as DicDHPR could bind to both substrates quinonoid-BH2 and quinonoid-DH2 by docking calculations and have confirmed their catalytic activity by in vitro assay.Structured summary of protein interactionsDHPRbindstoDHPR by X-ray crystallography(View interaction