6KOL

Crystal structure of auracyanin from photosynthetic bacterium Roseiflexus castenholzii

Summary for 6KOL

• Entry DOI: 10.2210/pdb6kol/pdb
• Descriptor: Blue (Type 1) copper domain protein, COPPER (II) ION, CHLORIDE ION, ... (4 entities in total)
• Functional Keywords: auracyanin, roseiflexus castenholzii, electron transfer, blue copper protein, metal binding protein
• Biological source: Roseiflexus castenholzii (strain DSM 13941 / HLO8)
• Total number of polymer chains: 1
• Total formula weight: 13336.20

Authors

Wang, C.,Zhang, C.Y.,Min, Z.Z.,Xin, Y.Y.,Xu, X.L. (deposition date: 2019-08-12, release date: 2020-01-29, Last modification date: 2023-11-22)

Primary citation

Wang, C.,Xin, Y.,Min, Z.,Qi, J.,Zhang, C.,Xu, X.
Structural basis underlying the electron transfer features of a blue copper protein auracyanin from the photosynthetic bacterium Roseiflexus castenholzii.
Photosyn. Res., 143:301-314, 2020

PubMed Abstract: Auracyanin (Ac) is a blue copper protein that mediates the electron transfer between Alternative Complex III (ACIII) and downstream electron acceptors in both fort chains of filamentous anoxygenic phototrophs. Here, we extracted and purified the air-oxidized RfxAc from the photoheterotrophically grown Roseiflexus castenholzii, and we illustrated the structural basis underlying its electron transferring features. Spectroscopic and enzymatic analyses demonstrated the reduction of air-oxidized RfxAc by the ACIII upon oxidation of menaquinol-4 and menaquinol-7. Crystal structures of the air-oxidized and Na-dithionite-reduced RfxAc at 2.2 and 2.0 Å resolutions, respectively, showed that the copper ions are coordinated by His77, His146, Cys141, and Met151 in minor different geometries. The Cu-S bond length increase of Met151, and the electron density Fourier differences at Cu and His77 demonstrated their essential roles in the dithionite-induced reduction. Structural comparisons further revealed that the RfxAc contains a Chloroflexus aurantiacus Ac-A-like copper binding pocket and a hydrophobic patch surrounding the exposed edge of His146 imidazole, as well as an Ac-B-like Ser- and Thr-rich polar patch located at a different site on the surface. These spectroscopic and structural features allow RfxAc to mediate electron transfers between the ACIII and redox partners different from those of Ac-A and Ac-B. These results provide a structural basis for further investigating the electron transfer and energy transformation mechanism of bacterial photosynthesis, and the diversity and evolution of electron transport chains.

PubMed: 31933173
DOI: 10.1007/s11120-020-00709-y

Experimental method

X-RAY DIFFRACTION (2.211 Å)