Complex structure of NADPH-cytochrome P450 reductase and heme oxygenase-1

NADPH-cytochrome P450 oxidoreductase (CPR) supplies electrons to various heme proteins including heme oxygenase (HO), which is a key enzyme for heme degradation. Electrons from NADPH flow first to FAD in CPR, then to FMN in CPR, and finally to heme in the redox partner. For electron transfer from CPR to its redox partner, ``closed-open transition'' of CPR is indispensable because FMN in the closed conformation of CPR is covered by FAD-binding domain, thus FMN is not exposed to the surface in the closed conformation. Recently, Hamdane et al. determined the crystal structures of a hinge-shortened rat CPR variant (ΔTGEE), which favors an open conformation [1]. In the open conformation of CPR, FMN is exposed to the surface, thus this conformation appears to be favorable to interact with the redox partners, though no complex structure of CPR and its redox partner has been determined. Here, we demonstrate that ΔTGEE makes a stable complex with heme-rat HO-1 (rHO-1) complex and can support HO reaction, though its efficiency is extremely limited. Further we determine the crystal structure of ΔTGEE in complex with heme-rHO-1 at 4.3 Å resolution [2]. X-ray scattering and biochemical data suggest that the complex structure of ΔTGEE and heme-rHO-1 is similar to that of wild type CPR and heme-rHO-1. Distance between heme and FMN in this complex (6 Å) implies direct electron transfer from FMN to heme. On the other hand, FAD is far from FMN and heme, indicating that the ``closed-open transition'' of CPR is required for electron transfer from FAD to FMN.

Structure and Anion Exchangeability of Ni-Al-Type Layered Double Hydroxides

Layered double hydroxide (LDH) is one of promising inorganic materials for cleaning the environmental water polluted by toxic anions. The crystal structure of LDH is composed of the positively-charged metal hydroxide nanosheets and the anions with water molecules intercalated between the nanosheet layers. To put LDHs for practical use, it is necessary to understand why only special anions can be intercalated into the crystal structure from the aqueous solution. In this study, the anion exchange experiments and the synchrotron radiation x-ray powder diffraction measurements of Ni-Al-type LDHs of several kinds of Ni/Al ratios with chlorine and nitrate anions were performed to investigate the relationship between the anion exchange selectivity and crystal structures. The nitrate ion selectivity is normally poor in most of LDHs with different metal ions in the hydroxide nanosheet [1]. However, the nitrate ions were preferred to the chlorine ions in Ni-Al-type LDH when Ni/Al = 4, whereas the chlorine ions were selected when Ni/Al = 2. The crystal structure analysis revealed that the interlayer distance decreased and the thermal motion of the nitrate ions suppressed in Ni-Al-nitrate-type LDH with increasing the Ni/Al ratio, whereas those of the chlorine ions in Ni-Al-chlorine-type LDH increased and enhanced with increasing the Ni/Al ratio. These results indicate that the nitrate ions are more stable than the chlorine ions in the crystal structure of the Ni-Al-type LDH when the positive charge of the nanosheet is small, i.e. the number of anions is small. The short interlayer distance and the small thermal vibration of anions in the crystal structure are the key to understand the anion selectivity of LDH.