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Conservation of the structural and functional architecture of encapsulated ferritins in bacteria and archaea

DOI: 10.1042/BCJ20180922 DOI Help

Authors: Didi He (The University of Edinburgh) , Cecilia Piergentili (Newcastle University) , Jennifer Ross (The University of Edinburgh) , Emma Tarrant (Newcastle University) , Laura R. Tuck (The University of Edinburgh) , C. Logan Mackay (The University of Edinburgh) , Zak Mciver (Newcastle University) , Kevin J. Waldron (Newcastle University) , David J. Clarke (The University of Edinburgh) , Jon Marles-wright (The University of Edinburgh)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Biochemical Journal , VOL 476 , PAGES 975 - 989

State: Published (Approved)
Published: March 2019
Diamond Proposal Number(s): 9487

Open Access Open Access

Abstract: Ferritins are a large family of intracellular proteins that protect the cell from oxidative stress by catalytically converting Fe(II) into less toxic Fe(III) and storing iron minerals within their core. Encapsulated ferritins (EncFtn) are a sub-family of ferritin-like proteins, which are widely distributed in all bacterial and archaeal phyla. The recently characterized Rhodospirillum rubrum EncFtn displays an unusual structure when compared with classical ferritins, with an open decameric structure that is enzymatically active, but unable to store iron. This EncFtn must be associated with an encapsulin nanocage in order to act as an iron store. Given the wide distribution of the EncFtn family in organisms with diverse environmental niches, a question arises as to whether this unusual structure is conserved across the family. Here, we characterize EncFtn proteins from the halophile Haliangium ochraceum and the thermophile Pyrococcus furiosus, which show the conserved annular pentamer of dimers topology. Key structural differences are apparent between the homologues, particularly in the centre of the ring and the secondary metal-binding site, which is not conserved across the homologues. Solution and native mass spectrometry analyses highlight that the stability of the protein quaternary structure differs between EncFtn proteins from different species. The ferroxidase activity of EncFtn proteins was confirmed, and we show that while the quaternary structure around the ferroxidase centre is distinct from classical ferritins, the ferroxidase activity is still inhibited by Zn(II). Our results highlight the common structural organization and activity of EncFtn proteins, despite diverse host environments and contexts within encapsulins.

Subject Areas: Biology and Bio-materials

Instruments: I04-Macromolecular Crystallography , I24-Microfocus Macromolecular Crystallography


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