title: Chemistry at the protein-mineral interface in L-ferritin assists the assembly of a functional (μ3-oxo)Tris[(μ2-peroxo)] triiron(III) cluster.
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.
authors.affiliation: Department of Biotechnology, Chemistry, and Pharmacy, University of Siena, Siena 53100, Italy.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Pozzi
authors.affiliation: Centro di Risonanze Magnetiche, University of Florence, Sesto Fiorentino, Florence 50019, Italy.|Department of Chemistry, University of Florence, Sesto Fiorentino, Florence 50019, Italy.
authors.forename: Silvia
authors.identifier: 0000-0002-1924-5046
authors.initials: S
authors.lastname: Ciambellotti
authors.affiliation: Centro di Risonanze Magnetiche, University of Florence, Sesto Fiorentino, Florence 50019, Italy.|Department of Chemistry, University of Florence, Sesto Fiorentino, Florence 50019, Italy.
authors.forename: Caterina
authors.identifier: 0000-0002-1023-0067
authors.initials: C
authors.lastname: Bernacchioni
authors.affiliation: Department of Biotechnology, Chemistry, and Pharmacy, University of Siena, Siena 53100, Italy.
authors.forename: Flavio
authors.initials: F
authors.lastname: Di Pisa
authors.affiliation: Department of Biotechnology, Chemistry, and Pharmacy, University of Siena, Siena 53100, Italy; turano@cerm.unifi.it stefano.mangani@unisi.it.|Centro di Risonanze Magnetiche, University of Florence, Sesto Fiorentino, Florence 50019, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Mangani
authors.affiliation: Centro di Risonanze Magnetiche, University of Florence, Sesto Fiorentino, Florence 50019, Italy; turano@cerm.unifi.it stefano.mangani@unisi.it.|Department of Chemistry, University of Florence, Sesto Fiorentino, Florence 50019, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Turano
mesh_terms: D000818:Animals; D001052:Apoferritins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry; D006736:Horses / Q000378:metabolism; D006801:Humans; D007477:Ions / Q000737:chemistry; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D005296:Ferrous Compounds; D007477:Ions; D001052:Apoferritins; D007501:Iron
keywords: L-ferritin; X-ray; biomineralization; metallocluster; nucleation site