Role of the conserved Ser-Tyr-Lys triad of the SDR family in sepiapterin reductase.
Sepiapterin reductase (EC 1.1.1.153; SPR) is an enzyme involved in the biosynthesis of tetrahydrobiopterin; and SPR has been identified as a member of the NADP(H)-preferring short-chain dehydrogenase/reductase (SDR) family based on its catalytic properties for exogenous carbonyl compounds and molecular structure. To examine possible differences in the catalytic sites of SPR for exogenous carbonyl compounds and the native pteridine substrates, we investigated by site-directed mutagenesis the role of the highly conserved Ser-Tyr-Lys triad (Ser and YXXXK motif) in SPR, which was shown to be the catalytic site of SDR-family enzymes. From the analysis of catalytic constants for single- and double-point mutants against the triad, Ser and YXXXK motif, in the SPR molecule, participate in the reduction of the carbonyl group of both pteridine and exogenous carbonyl compounds. The Ser and the Tyr of the triad may co-act in proton transfer and stabilization for the carbonyl group of substrates, as was demonstrated for those in the SDR family. But either the Tyr or the Ser of SPR can function alone for proton transfer to a certain extent and show low activity for both substrates.
Fujimoto
K
K
Department of Biochemistry, Meikai University School of Dentistry, Sakado, 350-0283, Saitama, Japan.
Hara
M
M
Yamada
H
H
Sakurai
M
M
Inaba
A
A
Tomomura
A
A
Katoh
S
S
D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D017931:DNA Primers; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase