ABSTRACT
Anthocyanidin synthase (ANS), an iron(II) and 2-oxoglutarate (2OG) dependent oxygenase, catalyses the penultimate step in anthocyanin biosynthesis by oxidation of the 2R,3S,4S-cis-leucoanthocyanidins. It has been believed that in vivo the products of ANS are the anthocyanidins. However, in vitro studies on ANS using optically active cis- and trans-leucocyanidin substrates identified cyanidin as only a minor product; instead both quercetin and dihydroquercetin are products with the distribution being dependent on the C-4 stereochemistry of the leucocyanidin substrates.
Subject(s)
Flavonoids/metabolism , Oxygenases/metabolism , Chromatography, High Pressure Liquid , Crystallography, X-Ray , Decarboxylation , Models, Molecular , Molecular Conformation , Stereoisomerism , Substrate SpecificityABSTRACT
The activity of the transcription factor hypoxia-inducible factor (HIF) is regulated by oxygen-dependent hydroxylation. Under normoxic conditions, hydroxylation of proline residues triggers destruction of its alpha-subunit while hydroxylation of Asn(803) in the C-terminal transactivation domain of HIF-1 alpha (CAD) prevents its interaction with p300. Here we report crystal structures of the asparagine hydroxylase (factor-inhibiting HIF, FIH) complexed with Fe((II)), 2-oxoglutarate cosubstrate, and CAD fragments, which reveal the structural basis of HIF modification. CAD binding to FIH occurs via an induced fit process at two distinct interaction sites. At the hydroxylation site CAD adopts a loop conformation, contrasting with a helical conformation for the same residues when bound to p300. Asn(803) of CAD is buried and precisely orientated in the active site such that hydroxylation occurs at its beta-carbon. Together with structures with the inhibitors Zn((II)) and N-oxaloylglycine, analysis of the FIH-CAD complexes will assist design of hydroxylase inhibitors with proangiogenic properties. Conserved structural motifs within FIH imply it is one of an extended family of Fe((II)) oxygenases involved in gene regulation.
Subject(s)
DNA-Binding Proteins/metabolism , Nuclear Proteins/metabolism , Transcription Factors , Amino Acid Sequence , Crystallography, X-Ray , DNA-Binding Proteins/chemistry , Hypoxia-Inducible Factor 1 , Models, Molecular , Molecular Sequence Data , Nuclear Proteins/chemistry , Oxidation-Reduction , Protein Conformation , Sequence Homology, Amino AcidABSTRACT
Asparagine-803 in the C-terminal transactivation domain of human hypoxia-inducible factor (HIF)-1 alpha-subunit is hydroxylated by factor inhibiting HIF-1 (FIH-1) under normoxic conditions causing abrogation of the HIF-1alpha/p300 interaction. NMR and other analyses of a hydroxylated HIF fragment produced in vitro demonstrate that hydroxylation occurs at the beta-carbon of Asn-803 and imply production of the threo -isomer, in contrast with other known aspartic acid/asparagine hydroxylases that produce the erythro -isomer.