Crystal structure of the oxygenase component (HpaB) of the 4-hydroxyphenylacetate 3-monooxygenase from Thermus thermophilus HB8.
The 4-hydroxyphenylacetate (4HPA) 3-monooxygenase is involved in the initial step of the 4HPA degradation pathway and catalyzes 4HPA hydroxylation to 3,4-dihydroxyphenylacetate. This enzyme consists of two components, an oxygenase (HpaB) and a reductase (HpaC). To understand the structural basis of the catalytic mechanism of HpaB, crystal structures of HpaB from Thermus thermophilus HB8 were determined in three states: a ligand-free form, a binary complex with FAD, and a ternary complex with FAD and 4HPA. Structural analysis revealed that the binding and dissociation of flavin are accompanied by conformational changes of the loop between beta5 and beta6 and of the loop between beta8 and beta9, leading to preformation of part of the substrate-binding site (Ser-197 and Thr-198). The latter loop further changes its conformation upon binding of 4HPA and obstructs the active site from the bulk solvent. Arg-100 is located adjacent to the putative oxygen-binding site and may be involved in the formation and stabilization of the C4a-hydroperoxyflavin intermediate.
Kim
Seong-Hoon
SH
SPring-8 Center, RIKEN Harima Institute, Koto 1-1-1, Sayo-cho, Sayo-gun, Hyogo, Japan.
Hisano
Tamao
T
Takeda
Kazuki
K
Iwasaki
Wakana
W
Ebihara
Akio
A
Miki
Kunio
K
D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics