The 1.25 A crystal structure of sepiapterin reductase reveals its binding mode to pterins and brain neurotransmitters.
Sepiapterin reductase catalyses the last steps in the biosynthesis of tetrahydrobiopterin, the essential co-factor of aromatic amino acid hydroxylases and nitric oxide synthases. We have determined the crystal structure of mouse sepiapterin reductase by multiple isomorphous replacement at a resolution of 1.25 A in its ternary complex with oxaloacetate and NADP. The homodimeric structure reveals a single-domain alpha/beta-fold with a central four-helix bundle connecting two seven-stranded parallel beta-sheets, each sandwiched between two arrays of three helices. Ternary complexes with the substrate sepiapterin or the product tetrahydrobiopterin were studied. Each subunit contains a specific aspartate anchor (Asp258) for pterin-substrates, which positions the substrate side chain C1'-carbonyl group near Tyr171 OH and NADP C4'N. The catalytic mechanism of SR appears to consist of a NADPH-dependent proton transfer from Tyr171 to the substrate C1' and C2' carbonyl functions accompanied by stereospecific side chain isomerization. Complex structures with the inhibitor N-acetyl serotonin show the indoleamine bound such that both reductase and isomerase activity for pterins is inhibited, but reaction with a variety of carbonyl compounds is possible. The complex structure with N-acetyl serotonin suggests the possibility for a highly specific feedback regulatory mechanism between the formation of indoleamines and pteridines in vivo.
Auerbach
G
G
Max-Planck-Institut für Biochemie, Abt. Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried, Germany. auerbach@biochem.mpg.de
Herrmann
A
A
Gütlich
M
M
Fischer
M
M
Jacob
U
U
Bacher
A
A
Huber
R
R
D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D004926:Escherichia coli; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010071:Oxaloacetates / Q000378:metabolism; D017433:Protein Structure, Secondary; D011622:Pterins / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D018377:Neurotransmitter Agents; D010071:Oxaloacetates; D011622:Pterins; D011994:Recombinant Proteins; D009249:NADP; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase