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6p8k

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Escherichia coli Bacterioferritin Substituted with Zinc Protoporphyrin IX

Structural highlights

6p8k is a 12 chain structure with sequence from Escherichia coli K-12. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	X-ray diffraction, Resolution 1.7Å
Ligands:	, , ,
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Function

BFR_ECOLI Iron-storage protein, whose ferroxidase center binds Fe(2+) ions, oxidizes them by dioxygen to Fe(3+), and participates in the subsequent Fe(3+) oxide mineral core formation within the central cavity of the protein complex. The mineralized iron core can contain as many as 2700 iron atoms/24-meric molecule.^[1] ^[2]

Publication Abstract from PubMed

The iron storage protein bacterioferritin (Bfr) binds up to 12 hemes b at specific sites in its protein shell. The heme b can be substituted with the photosensitizer Zn(II)-protoporphyrin IX (ZnPP), and photosensitized reductive iron release from the ferric oxyhydroxide {[FeO(OH)]n} core inside the ZnPP-Bfr protein shell was demonstrated [Cioloboc, D., et al. (2018) Biomacromolecules 19, 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)]n. Femtosecond transient absorption spectroscopy shows that this photooxidation occurs from the singlet excited state ((1)ZnPP*) on the picosecond time scale and is consistent with two oxidizing populations of Fe(3+), which do not appear to involve the ferroxidase center iron. We propose that [FeO(OH)]n 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)]n would effectively cause migration of Fe(2+) 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(3+) reduction could be used to identify the sites of iron mobilization within the Bfr protein shell.

Structure of a Zinc Porphyrin-Substituted Bacterioferritin and Photophysical Properties of Iron Reduction.,Benavides BS, Valandro S, Cioloboc D, Taylor AB, Schanze KS, Kurtz DM Jr Biochemistry. 2020 Apr 28;59(16):1618-1629. doi: 10.1021/acs.biochem.9b01103., Epub 2020 Apr 16. PMID:32283930^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Yang X, Le Brun NE, Thomson AJ, Moore GR, Chasteen ND. The iron oxidation and hydrolysis chemistry of Escherichia coli bacterioferritin. Biochemistry. 2000 Apr 25;39(16):4915-23. PMID:10769150
↑ Baaghil S, Lewin A, Moore GR, Le Brun NE. Core formation in Escherichia coli bacterioferritin requires a functional ferroxidase center. Biochemistry. 2003 Dec 2;42(47):14047-56. PMID:14636073 doi:http://dx.doi.org/10.1021/bi035253u
↑ Benavides BS, Valandro S, Cioloboc D, Taylor AB, Schanze KS, Kurtz DM Jr. Structure of a Zinc Porphyrin-Substituted Bacterioferritin and Photophysical Properties of Iron Reduction. Biochemistry. 2020 Apr 28;59(16):1618-1629. PMID:32283930 doi:10.1021/acs.biochem.9b01103