6P8L

Escherichia coli Bacterioferritin Substituted with Zinc Protoporphyrin IX (Zn Absorption Edge X-ray Data)

Summary for 6P8L

• Entry DOI: 10.2210/pdb6p8l/pdb
• Descriptor: Bacterioferritin, ZINC ION, SODIUM ION, ... (6 entities in total)
• Functional Keywords: bacterioferritin, zinc protoporphyrin ix, photosensitizer, ferritin, metal binding protein, oxidoreductase
• Biological source: Escherichia coli K-12
• Total number of polymer chains: 12
• Total formula weight: 229706.65

Authors

Taylor, A.B.,Cioloboc, D.,Kurtz, D.M. (deposition date: 2019-06-07, release date: 2020-05-13, Last modification date: 2023-10-11)

Primary citation

Benavides, B.S.,Valandro, S.,Cioloboc, D.,Taylor, A.B.,Schanze, K.S.,Kurtz Jr., D.M.
Structure of a Zinc Porphyrin-Substituted Bacterioferritin and Photophysical Properties of Iron Reduction.
Biochemistry, 59:1618-1629, 2020

PubMed Abstract: The iron storage protein bacterioferritin (Bfr) binds up to 12 hemes at specific sites in its protein shell. The heme can be substituted with the photosensitizer Zn(II)-protoporphyrin IX (ZnPP), and photosensitized reductive iron release from the ferric oxyhydroxide {[FeO(OH)]} core inside the ZnPP-Bfr protein shell was demonstrated [Cioloboc, D., et al. (2018) , 178-187]. This report describes the X-ray crystal structure of ZnPP-Bfr and the effects of loaded iron on the photophysical properties of the ZnPP. The crystal structure of ZnPP-Bfr shows a unique six-coordinate zinc in the ZnPP with two axial methionine sulfur ligands. Steady state and transient ultraviolet-visible absorption and luminescence spectroscopies show that irradiation with light overlapping the Soret absorption causes oxidation of ZnPP to the cation radical ZnPP only when the ZnPP-Bfr is loaded with [FeO(OH)]. Femtosecond transient absorption spectroscopy shows that this photooxidation occurs from the singlet excited state (ZnPP*) on the picosecond time scale and is consistent with two oxidizing populations of Fe, which do not appear to involve the ferroxidase center iron. We propose that [FeO(OH)] clusters at or near the inner surface of the protein shell are responsible for ZnPP photooxidation. Hopping of the photoinjected electrons through the [FeO(OH)] would effectively cause migration of Fe through the inner cavity to pores where it exits the protein. Reductive iron mobilization is presumed to be a physiological function of Bfrs. The phototriggered Fe reduction could be used to identify the sites of iron mobilization within the Bfr protein shell.

PubMed: 32283930
DOI: 10.1021/acs.biochem.9b01103

Experimental method

X-RAY DIFFRACTION (2.1 Å)