Nucleation of the iron core occurs at the three-fold channels of horse spleen apoferritin: an EXAFS study on the native and chemically-modified protein.
Extended X-ray absorbance fine structure measurements have been carried out on the initial Fe(III)-apoferritin complex at a Fe/subunit ratio of 2 in native and modified horse spleen apoferritin. Analysis of the data indicates that in the native protein the iron forms a protein-bound polynuclear cluster (Fe-Fe distance 3.4 A) with a first coordination sphere constituted by 5-6 low-Z atoms, e.g., nitrogen atoms, carboxylate-like ligands or oxo bridges between the iron atoms. Modification of Cys-126, a residue localized on the outer surface of the hydrophilic three-fold channels, with p-chloromercuribenzoate (PMB) or phenylmercuric acetate (PMA) brings about distinctive differences. In particular, in the PMB-reacted protein the feature assigned to the iron-iron interaction disappears from the spectrum, whilst in the PMA-reacted protein the main differences with respect to the native protein are observed at the level of the first coordination sphere. These results confirm the formation of protein-Fe(III)-clusters and localize these sites at the hydrophilic three-fold channels of horse spleen apoferritin.
Strange
R
R
Daresbury Laboratory, Warrington, UK.
Morante
S
S
Stefanini
S
S
Chiancone
E
E
Desideri
A
A
D000818:Animals; D001052:Apoferritins / Q000737:chemistry*; D001665:Binding Sites; D006736:Horses; D007501:Iron / Q000737:chemistry*; D010662:Phenylmercuric Acetate; D013154:Spleen / Q000737:chemistry*
D001052:Apoferritins; D007501:Iron; D010662:Phenylmercuric Acetate