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Chemistry at the protein–mineral interface in L-ferritin assists the assembly of a functional (μ 3 -oxo)Tris[(μ 2 -peroxo)] triiron(III) cluster

DOI: 10.1073/pnas.1614302114 DOI Help

Authors: Cecilia Pozzi (University of Siena) , Silvia Ciambellotti (University of Florence) , Caterina Bernacchioni (University of Florence) , Flavio Di Pisa (University of Siena) , Stefano Mangani (University of Siena) , Paola Turano (University of Florence)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Proceedings Of The National Academy Of Sciences , VOL 114 , PAGES 2580 - 2585

State: Published (Approved)
Published: March 2017
Diamond Proposal Number(s): 11690

Open Access Open Access

Abstract: X-ray structures of homopolymeric L-ferritin obtained by freezing protein crystals at increasing exposure times to a ferrous solution showed the progressive formation of a triiron cluster on the inner cage surface of each subunit. After 60 min exposure, a fully assembled (μ3-oxo)Tris[(μ2-peroxo)(μ2-glutamato-κO:κO′)](glutamato-κO)(diaquo)triiron(III) anionic cluster appears in human L-ferritin. Glu60, Glu61, and Glu64 provide the anchoring of the cluster to the protein cage. Glu57 shuttles incoming iron ions toward the cluster. We observed a similar metallocluster in horse spleen L-ferritin, indicating that it represents a common feature of mammalian L-ferritins. The structures suggest a mechanism for iron mineral formation at the protein interface. The functional significance of the observed patch of carboxylate side chains and resulting metallocluster for biomineralization emerges from the lower iron oxidation rate measured in the E60AE61AE64A variant of human L-ferritin, leading to the proposal that the observed metallocluster corresponds to the suggested, but yet unobserved, nucleation site of L-ferritin.

Journal Keywords: L-ferritin, metallocluster, nucleation site, biomineralization

Subject Areas: Chemistry

Instruments: I03-Macromolecular Crystallography

Other Facilities: Elettra Synchrotron Trieste