2D36: The Crystal Structure Of Flavin Reductase Hpac

4-Hydroxyphenylacetate (4-HPA) is oxidized as an energy source by two component enzymes, the large component (HpaB) and the small component (HpaC). HpaB is a 4-HPA monooxygenase that utilizes FADH(2) supplied by a flavin reductase HpaC. We determined the crystal structure of HpaC (ST0723) from the aerobic thermoacidophilic crenarchaeon Sulfolobus tokodaii strain 7 in its three states [NAD(P)(+)-free, NAD(+)-bound, and NADP(+)-bound]. HpaC exists as a homodimer, and each monomer was found to contain an FMN. HpaC preferred FMN to FAD because there was not enough space to accommodate the AMP moiety of FAD in its flavin-binding site. The most striking difference between the NAD(P)(+)-free and the NAD(+)/NADP(+)-bound structures was observed in the N-terminal helix. The N-terminal helices in the NAD(+)/NADP(+)-bound structures rotated ca. 20 degrees relative to the NAD(P)(+)-free structure. The bound NAD(+) has a compact folded conformation with nearly parallel stacking rings of nicotinamide and adenine. The nicotinamide of NAD(+) stacked the isoalloxazine ring of FMN so that NADH could directly transfer hydride. The bound NADP(+) also had a compact conformation but was bound in a reverse direction, which was not suitable for hydride transfer.
PDB ID: 2D36Download
MMDB ID: 39170
PDB Deposition Date: 2005/9/26
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2.3  Å
Source Organism:
Similar Structures:
Biological Unit for 2D36: dimeric; determined by author and by software (PISA,PQS)
Molecular Components in 2D36
Label Count Molecule
Proteins (2 molecules)
Hypothetical Nadh-dependent FMN Oxidoreductase
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

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